I have 40 batteries in a 48 volt battery bank. These are 30 lb each lead acid gel cells. The specs on the side of the cases reads. 12v, 150w/cell, 15 min.
How many amp hrs do I have at 48 volts? They are configured 10 rowes perelelled of 4 each in siries. Befor I take some heat about gel cells, 2 things. they were free and like new. This 1200 LB bank should have a few AH.
At face value, 40 batteries in 48 volt bank, each being 12V would indicate 10 parallel strings of 4 series batteries each. *DOH* You already said that.
150W/cell doesn't make any sense.
Based on my own 2V/500AH SLA cells, around 30 watthours/Kg energy density, your batteries are 13Kg each suggests about 400 WH per battery, or around 30 amphours per battery.
IF all these assumptions are right, you have 320 amphours @ 48V. But for maximum battery life, you don't want to discharge them more than about 10-20% of that, so you probably have a bank you could regularly use to around 30-40 amphours discharge (2000 watt-hours, give or take).
Edit: Actually, 150W, 15 mins.... 150W @ 12V = 12.5 amps.
12.5 amps for 15 minutes = 3.125 amp-hours.
that's about exactly 1/10 the estimated cell capacity..... coincidence?