I don't know about you guys, but 5.7V sounds well below a normal "resting voltage" for a 12V battery. There may be some other issues, but it sounds like your battery might be bad.

If you are going to let the car sit, I recommend getting a Battery Minder. Keeps the battery topped up without chance of overcharging it. Comes with a little cable/plug which you permanently attach to your battery posts, and just plug and unplug the charger when you need it. I get mine at Batterymart.com as this is the lowest price I have found (no vested interest in either the product or the vendor). Costs only a few cents per month to run 24/7.

Worst thing for a lead-acid battery is to charge-discharge cycle it. Causes sulfation of the plates, and you will never again get full battery capacity. Lead-acid batteries like to be kept fully charged at all times for longest service life.

Tom

 

How long did you drive for after you installed it? The dry charge they come with isn't very strong.

 

I drove it quite a bit after installing the redtop. Normally, I drive it at least weekly (I come up with reasons to drive it). But I haven't recently, since it's in the middle of a suspension upgrade and a bit off balance.
I'm getting it towed to exotic motorwerks tomorrow for some suspension work (and now the just discovered fuel leak issue), I'll ask them what they think, and if they have a high current ammeter to check it.

I'm actually glad the battery died, since I might not have discovered my fuel leak otherwise.