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Discussion Starter · #1 · (Edited)
For those looking to remove weight especially up front you can replace the stock battery with a $200 Braille B2015 Battery which weighs 15 lbs. The stock battery weighs 30 lbs.

The 2014 6 owners manual says you need to replace the stock battery with a battery with at least 20 amp-hour rating. The B2015 has a 21 amp hour rating so it is good enough for general power drains "deep cycling". The biggest issue with the Braille batteries is low cold cranking amps, so if you typically start your car in sub freezing or sub zero it may not work real well.

I'm in San Diego, and coldest weather I've started in so far is about 55 degrees, and the starter turns over fast as stock. I just custom installed it on the factory batter tray as shown in the attached photo using a 1/4" eyelet bolt and 1" x .125" aluminum bar and 1/4"bolts and nuts from Home Depot.

Here is Braille's data for my battery:
http://www.braillebattery.com/index.php/braille/product_batteries/b2015

"At under 15 pounds, the B2015 is out most popular non-carbon racing battery. It is able to start larger engines easily for racing and offers daily driving capability for 4 cylinder motors with ease."

Voltage 12
Full Charge Voltage 13.2
Pulse Cranking Amps (PCA) 1067
Cranking Amps (CA) 574
Amp Hour (AH) 21
Cold Cranking Amps (CA) 426
Reserve Capacity (RC) 35 mins.
Life Cycle @ 10% DOD 3100
 

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Interesting. For the small size/weight of a Braille, what if you connect two side by side, in parallel. Imagine the boosted current/amperage, yet still provide 12V to the car's electricals..but then, you'd defeat the weight savings purpose. :)
 

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Discussion Starter · #3 ·
Quick update:
I went on a vacation and did not drive the car for 8 days, left the Braille 2015 Battery connected to the car. Ambient in the garage was probably around 60deg average.

It turned over the engine just like I'd left it only overnight. This battery continues to perform like stock minus 15lbs of weight.
 
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Quick update:
I went on a vacation and did not drive the car for 8 days, left the Braille 2015 Battery connected to the car. Ambient in the garage was probably around 60deg average.

It turned over the engine just like I'd left it only overnight. This battery continues to perform like stock minus 15lbs of weight.
What would happen with the battery that's only 10 amp/hour?
 

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Discussion Starter · #5 · (Edited)
What would happen with the battery that's only 10 amp/hour?
From what I gathered on a BMW 5 series message board where they ran way undersized brailles they died after a few weeks. It's probably a matter of the base level power draw for modern cars which drains quite a bit, then cranking over the engine when it's already kind of depleted. In english, a too small battery gets excessively deep cycled every night and fails in a very short period of time.

I've had mine which meets the factory rating for 6 months and it's been completely uneventful.
 

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With a battery that under-rated you also run the risk of all sorts of electrical shenanigans that can drive you nuts. Just went through that with my formula.. blah. Chased O2 sensors, wires, TPS, MAF, basically every sensor I have left except for cam sensor and OPSU LOL. Then I found the culprit after grabbing the multimeter and testing the battery itself -.-
Though, that may only be an issue when VOLTAGE is low, and not just amperage. I'm not entirely sure about that one.
 

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Discussion Starter · #7 ·
I just got back from a long vacation. My car sat for 18 days. When it started it was sluggish turning over. The headlights were on when it turned over, which probably didn't help. So 2.5-3 weeks is about all the battery can take of parasitic drain when not being used.
 

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Discussion Starter · #8 ·
Okay, another update.

I took my daughter to preschool in the morning yesterday and she turned on the dome light in the back and didn't turn it off and I didn't know it. I came back to my car 10 hours later after work and realized it when it was dark out. I tried to start the car, and it tried to turn over but it didn't have enough juice.

Being AGM I was concerned about jumping it with somebody else's car and didn't feel like calling and waiting for AAA, so I took advantage of having a manual transmission and with a little help got it pushed down a gentle slope, and popped the clutch temporarily in 2nd gear and pressed the starter button and walla, engine was running. I drove the car for about 15 minutes staying in lower gears than normal to keep the revs up on the alternator.

When I started the car this morning it turned over fine in my 55 degree garage.

I was just reading up on recharging the Miata's AGM panasonic battery and it states in may need avery long time to recharge on the alternator if it drains, because the current levels it allows for recharging are so low. So recharging adequately in 15 minutes is pretty good I guess.

I continue to be quite satisfied with this battery. It carries as much real world reserve as any other car battery I've ever had, and recharged okay from a resonably deep discharge. These batteries are supposed to last 6-10 years so I will eventually know if the deep discharges affect it's life. This is the first time, and realistically won't be the last.

One final shoutout to another long lost advantage of a MTX...being able to restart an engine with a drained battery!
 

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AGMs will take charge at a RIDICULOUS rate; your information is exactly backward.

The big risk with jumping it is that significant arcing can occur when you make the final connection due to the extremely low internal resistance of those batteries. Make damn sure (1) the jumping car is running and (2) you make the last connection to a solid point on the block (e.g. electrical ground), NOT the battery. While AGMs should not outgas and thus should not explode "should" isn't good enough in a situation like this.

I'm surprised the dome lights are not body-module protected against being left on like this; my Jetta is and it's an 03!
 

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Discussion Starter · #10 · (Edited)
Somebody on the Miata website purported to have a letter from Panasonic about the oem battery. Could be unique to that battery. I have read many places that when recharging AGMs with the portable charger to use a lower current. That's probably where the misconception comes in. You need to purposely charge it at a lower current because the battery doesn't have the resistance to slow down the re-charge rate to a reasonable level.

Thanks for the clarification.

The lower interior lights that come on when a door is open turn off after a while if you leave the door open too long. outside lights are auto-off. Just the Dome lights aren't auto off when they've been manually turned on. Very dangerous for those of us with kids...
 

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I have read many places that when recharging AGMs with the portable charger to use a lower current. That's probably where the misconception comes in. You need to purposely charge it at a lower current because the battery doesn't have the resistance to slow down the re-charge rate to a reasonable level.
Bee-ess.

Any charger worth anything is amp-regulated for its OWN safety -- that is, it won't charge into a dead short, it will either trip (e.g. circuit breaker) or regulate down to what it can deliver safely.

The big risk with AGMs is that if you overcharge them they will outgas and that's permanently damaging since there is no way to replace the electrolyte that is lost when it happens -- they're valved and should NEVER vent.

But is very, very difficult to overcharge an AGM during the bulk charge phase as they can take outrageous charge currents without material heating due to their very low internal resistance. Many can accept charge during the bulk phase at 5C (e.g. 400 amps for an 80AH battery!) without damage -- IF the charger can deliver it. Where the risk shows up is when you don't have a proper 3-stage charging source that fails to honor the change to absorption from bulk (~14.4V @ 70F); at that point the charger needs to switch to constant-VOLTAGE mode until the current drops to ~1% of the amp-hour rating, at which point the battery is "full."

I believe my Jetta has body module override for the dome lights even if manually turned on..... I'm reasonably sure I've done that in the past and did not come back to find a dead battery.
 

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Discussion Starter · #12 · (Edited)
The manual action to turn on the dome lights individually is just a contact switch so no reason it couldn't be set to turn off like everything else. It may have just been an oversight, or they didn't care enough to worry about it. Either way it's dangerous to your battery.

It sounds like it is pretty safe to jump an AGM battery as long as you just charge enough to get the engine to turn over and let the alternator do the rest.
 

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It sounds like it is pretty safe to jump an AGM battery as long as you just charge enough to get the engine to turn over and let the alternator do the rest.
Yes, but do drive the car for a while after doing that. Remember that getting to ~80% of capacity is quick with an AGM but once you get there the battery goes into absorption charge (if the regulator is worth anything) and that takes over an hour (typically closer to two hours) to "finish it up." You want to get that last 15% or so in the battery; not finishing the cycle repeatedly risks losing that capacity permanently.
 

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Discussion Starter · #14 ·
AGMs will take charge at a RIDICULOUS rate; your information is exactly backward.

The big risk with jumping it is that significant arcing can occur when you make the final connection due to the extremely low internal resistance of those batteries. Make damn sure (1) the jumping car is running and (2) you make the last connection to a solid point on the block (e.g. electrical ground), NOT the battery. While AGMs should not outgas and thus should not explode "should" isn't good enough in a situation like this.

I'm surprised the dome lights are not body-module protected against being left on like this; my Jetta is and it's an 03!
Tickerguy thanks for the advice, I had to use it last night and it worked.

I had an unsuccessful attempt to flash update my ecu, and accidentally left my power converter plugged into the car (turned on) and to my laptop with it's 7 year old battery. I took my other car to work and when I got home the battery was so drained the dome lights were a dim shade of amber with no instrument display at all. So I had a dead battery and a blank ECU!

So I jumped in two steps. One steps to get enough juice in the battery to be able to flash the ECU with the tune and another to get the car started. I've put about 1.5 hours of driving on it since then, and it seems to be turning over fine.

So hopefully this battery didn't get too damaged from this incident. I will see eventually. But so far this battery continues to be a tough battery, that does everything I need it to, of course I don't have to cold start in freezing temperatures which may severly challege it.
 

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That battery seams like it was made by Timex LOL.
 

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You have almost-certainly done a quite-material amount of damage to the battery's AH capacity but the good news is that a flooded battery would likely have been effectively killed with this abuse.

AGMs tolerate this sort of thing a lot better....
 

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Discussion Starter · #17 ·
Yeah, I probably did damage it substantially. Even after 15 minutes hooked up to another car running, it still sparked good when I removed the jumper cables and woildn't come close to turning over. I thought for sure it was a gonner, but it did turn over after the first driving odyssey, and the more I drove it the better it turned over to where it is back to normal now, but that isn't that encouraging. Will it strand me if I do some parking lot hopping? Who knows what the Amp hours left are. Factory recommends 20 this HAD 21...

I'll probably have to disconnect it when I go on vacation and other conscientious stupid stuff like that. And at some point well short of my original 8-10 years expectation I'll have to replace it. Bummer.

At least I've fully vetted this battery as a correct lightweight battery option for this car and it will be extremely easy to replace it when it dies since the hard effort of making a solid installation for it is already done. $200 is a lot of money for a battery but with 2 or more lives compared to a standard battery it makes it a reasonable way to reduce weight at the front end of this car.
 

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At least I've fully vetted this battery as a correct lightweight battery option for this car and it will be extremely easy to replace it when it dies since the hard effort of making a solid installation for it is already done. $200 is a lot of money for a battery but with 2 or more lives compared to a standard battery it makes it a reasonable way to reduce weight at the front end of this car.
Drop the OEM battery back in, and just take off the front bumper. Replace with some 3M film + a few zipties. That stuff's indestructible, and the bumper is heavy. :grin2:

or, for the stealth look, just remove the steel reinforcement behind the bumper skin. >:)

Seriously - thanks for being the guinea pig on this one - I'm not ready to take the plunge for just 15lb (i'd be better served removing that same weight from the driver's midsection), but when my OEM battery needs replacing, this will be on the short list.
 

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Just pay close attention to cranking speed when the car is left unused for a couple of days. If you start to notice a bit of a slowdown..... you're in trouble.

Amp-hours are almost immaterial in terms of starting. It's instantaneous amp delivery that starts the car; 500 amps for 5 seconds to crank is less than one amp-hour, but delivering those 500 amps at 12V requires a total system resistance (including across the battery terminals) of 0.024 ohms!

Amp-hours are what you consume when in accessory (engine off) or if your alternator dies while driving.

You can lose all but a few amp-hours in a battery and still start the car. Develop ANY material internal resistance in the battery, however, and you can't get the instantaneous amps required to crank.
 
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