rin67630 wrote: ↑
Tue Oct 15, 2019 10:03 am
davidcoton wrote: ↑
Tue Oct 15, 2019 8:23 am
Leisure batteries (sold for caravans, for example) are a better buy for this purpose.
Are they not less common and hence more expensive at same capacity?
Less common yes. More expensive for the stated nominal capacity, yes. The point is they are less expensive for the useful capacity, because you'll need a bigger nominal capacity starter battery to deliver the desired performance.
A starter battery has a nominal capacity but if you actually drain a significant proportion of that (say, more than 30%) more than a few times you'll wear out the battery. A leisure (or 'deep cycle') battery should deliver close to its stated capacity many times. If you buy a starter battery you'll need to buy one with a much bigger number on the side, and then it won't be cheaper.
There's no hard changeover between a starter battery and a leisure battery - it's a continuum of behaviour between things that will do very high currents for short periods and don't like being run down, to things that will do low currents for long periods but don't mind being drained relatively low.