# 12 Volt Accessory Battery recommendations



## morse90 (Mar 23, 2010)

Hi there,

My 12 volt accessory battery in my Sera EV is dying mainly due to high draw from vacuum brake pump. The battery is standard 12 volt lead acid car battery about 45ah. It is dying due to high draw and is charged by the alternator which works only when EV is driving. This has lasted well with occasional top ups with 12 volt battery charger when doing a lot of driving in traffic with headlights, stereo etc. Wondering what people recommend these days that is not to costly and easy to get hold of in Auckland as a replacement. The vaccum pump pulls about 65amps when presurising the brake system when running so am thinking thats why after a year the battery has had enough and is starting to drop voltage rapidly even when charged with 12 volt charger every now and then.

Cheers
Theo


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## Ziggythewiz (May 16, 2010)

How big is the one you have?

I used a 125AH Marine DC batt for a couple years that was great, then tried to skimp on the weight a little and went with a 80AH or something and it's crap.


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## carrott (Aug 19, 2008)

morse90 said:


> My 12 volt accessory battery in my Sera EV is dying mainly due to high draw from vacuum brake pump. The battery is standard 12 volt lead acid car battery about 45ah. It is dying due to high draw and is charged by the alternator which works only when EV is driving. This has lasted well with occasional top ups with 12 volt battery charger when doing a lot of driving in traffic with headlights, stereo etc.


I think you might find that it is not the high current that killed your battery but rather the deep discharge. A normal car battery is very good at high current and very poor at deep discharge. It's designed to start the car and then be immediately recharged and to always live at a high state of charge.

If you're regularly discharging deeply because your alternator isn't turning when the car is stopped and perhaps isn't turning fast enough when the car is in motion, then it's going to have a hard life. What were they symptoms that caused you to top it up with an external charger?

If you stick with lead acid, get a large deep cycle battery or install a small-ish dc-dc to help when the alternator isn't turning or charge the accessory battery with a good charger every time you charge the traction battery.

If you get a lithium accessory battery you should have fewer problems. I guess a bottom balanced battery will work, so long as the alternator doesn't overcharge it, if the alternator produces 14.4V then you're very likely to have problems with bottom balance, while 13.8V might work ok.


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