Deep cycle or starter battery charging issues

TURNKEY wrote:
Also I'm concerned with the charge rate I can use to charge the batteries. The greater the charge amps the less time to recharge BUT I was told deep cycle batteries are best charged slowly.

It sounds like you were told that because deep cycle batteries are best charged slowly, you should not use them. That's wrong. Your application is perfect for deep cycle. Starting Lighting Ignition (SLI) batteries aren't designed for deep discharge. You would be far more likely to damage SLI batteries by discharging them too far than you would be to damage a deep cycle by charging at too high a rate.

I gather from the above posts that if I have more batteries given a set amount of useage they will each draw down less

This part is correct. Batteries last longer when each discharge cycle is less deep, so this means that the batteries will last longer.

and therefore can be charged to full capacity faster,

You were worried about charge rate limits. A typical charge rate limit is the total battery bank capacity C divided by 5. By using more batteries you increase total C and increase the allowable maximum charge rate. By adding batteries to the bank you also increase how much power you can draw out (you don't run out of power in the middle of a cold night) and decrease the wear and tear on each individual battery (cycling a single battery down to 80% discharged is much harder on it than cycling two batteries down to 40% discharged).

BUT if I use the same charger in both situations, given it has a set output, won't the resulting charge time be the same?????

You have to consider how rapidly the battery will accept the charge current. If I buy a single 100AH battery, I can only charge at 20A for C/5. If I buy two I can charge at 40A and if I buy 4 I can charge at 80A. That's the maximum rate, and above about 80-90% charged, the batteries won't even accept that much.

If I've used 80 AH and want to restore it by running my gen the minimum time, I'd much prefer recharging four batteries at nearly 80A than a single battery at only 20 amps. Of course, if you only have a 20A charger and only use 10-20AH between charges, then there's no need to buy a 400AH battery bank. Ideally, you want to use no more than about 50% of your capacity and never more than 80% between charges. Knowing how much capacity you need is the first step.