Battery RC question

[PCDOC]

Adding a house battery to the boat. Interstate group 29 with a reserve capacity of 210. Just wanted to see if my math is right. Let's say I am drawing 8 amps from the battery. I came up with just under 11 hours to hit the rc of 210. Sound right or am I missing something?

Thanks

[jhebert]

The definition of the specification of RESERVE CAPACITY (RC) is as follows:

Reserve Capacity (RC) is the number of minutes a fully charged battery at 80-degrees-F will discharge 25-Amperes until the battery drops below 10.5 volts.

The battery under discussion has an RC rating of 210-minutes, or 3.5-hours. I believe you are extrapolating that to your new figure of about 11-hours based on the ratio of the current, 25/8. To convert that RC figure to Ampere-hours, we'd use 25-Amperes and 3.5-hours and come up with 87.5-Ampere-hour (A-h). Then at 8-Amperes, we'd estimate 10.9-hours.

I suspect that at the substantially lower current discharge rate of 8-Amperes, the battery may provide longer service than the 11-hours you calculate. You should check the manufacturer's specifications for the battery to see if there is an Ampere-hour rating at lower current discharge rate than 25-Amperes. In any case, your figure of about 11-hours is probably a conservative rating. On the other hand, you are going to have a very deeply discharged battery at that point.