Dan,
All hooked together, you should have ~585 Amp-hours at 12 V. If your generator (do you mean petrol or wind ? - the following comments assume petrol) is only charging them to 13.23 V, it will shorten their lives since they are not getting fully charged. Or do you mean 13.23 V residual after you've disconnected the genny ? What kind of charge control are you using ?
Mind you, it is possible to charge them fully at 13.23 V, but it will take many hours, which is a waste of fuel. Your charger (for 585 Ah of battery) should put out a minimum of 15 A to charge them fully (20-30 A would be better), and it should regulate them to 14.4 V to get it done in a reasonable amount of time. An auto battery is regulated at 13.8 V, but that is a different kind of battery !
Ideally 3-stage charging is best, where the 3 stages are:
- Bulk charge (all amps possible from the charging source) until the absorption threshold voltage (usually 14.4 V per 12 V nominal or 2.4 V per cell for flooded lead acid batteries) is reached.
- Absorption charge at the absorption threshold (voltage regulated and with a tapering current). This usually lasts 2-4 hours or when a threshold low current is reached which will maintain the absorption voltage.
- Float, where the current is further reduced to maintain a float charge indefinitely (usually 13.2-13.4 V per 12 V or 2.2 V per cell). This is for a solar charge controller; a petrol generator charge should skip this step and stop here.
For a wind generator, which often doesn't have the daily regimen that solar has (and thus has more contiguous hours available sometimes, albeit not at as constant a charge rate), the absorption charge is often skipped, going directly to float, but the float voltage is higher, generally around 13.6-13.8 V per 12 V or 2.3 V per cell.
OK, probably more than you asked for (and maybe not even pertinent to your situation), but sometimes I can't do things by little bits !
Best Regards,
Dave