Adding a 2nd battery in the trunk in parallel, as a backup
 

I have a small battery (similar to an odyssey 680) under the hood. Works well,but the parasite discharge of some of the car components make the battery not '100percent' and given the fact that I don't use it all the time also doesn't help the matter.

I'm thinking of putting an extra optima battery in the trunk in a parallel fashion, so that I would have two batteries (under hood and in the trunk) so I won't need to worry about discharge and any other issues related to a powersport battery / small battery.

If I were to track the car, I could remove the battery in the trunk to save weight and in the winter I could remove the lithium battery (bring it indoors) and just trickle charge the optima. That way I could start the car once in a while in the winter time.

Has anyone done this?

I saw one post on the forum, but the guy just had an extra battery for backup with no intention of removing it.

Does this sound like a dumbass idea?

Lithium batteries don't work well with low constant draws. If you can't fix your parasitic loss issues I'd just run a larger battery in daily driving, and just swap the lighter battery when you go to track.

Get a decent battery to begin with. Then, as you say you don't drive it often, get a computer charger ( some can be mounted in car) and keep it topped off that way. You will then have a perfect battery to start and drive with.

Mounting a battery in the trunk has problems. The current required of the battery demands pretty substantial, very long cable runs. Weight, expense, and hassle. You will have issues with securing a battery in the trunk, keeping in mind the buildup of explosive gasses, and acid spills. You also can have problems with one battery failing and causing the other battery to drain thus defeating the purpose you state you have in mind. Lastly, it impacts limited cargo space. Forget it.

I use the XS power S680(pc680 rival) as my sole battery in my occasional use s2000. I've gone about two months in between starts before and have never noticed any slow starts. I don't trickle charge it or keep a tender on it, just use it as a conventional battery and never have had any issues. I'd just recommend keeping what you have and eliminating your parasitic draw issues.

Why don't you start with a parasitic draw test to see how much you're drawing? Shouldn't be more than 30mA.

if you have that much of a drain issue it would most likely drain a second battery as well. I would just unhook the battery when not using the car for more then a couple days

Just add a battery cut off switch and turn it off for long periods of storage. That is what I did in the wifely unit's portable condo when the smoke detector and CO detector were killing the battery.

http://www.racerpartswholesale.com/p...ry_Disconnects

Battery cut out has it own issues. ECU will loose its memory, radio presets, radio security code if still using stock.

I vote for Battery Tender. They sell a plig in connector you can wire into your battery terminals, and you can have plug exposed in grill area or other convenient location. Then when extended parked, just plug your Tender into the cars plug.

The Tender plug is really just a trailer hitch plug, so you also roll your own if so inclined.