When using lead acid batteries (which includes SLA and AGM), you run the risk of significantly reducing the available charge cycles by continually discharging below 50% or 12.2 volts. When calculating your expected Ah, also take into consideration that, when recharging daily via solar (or in my case an alternator), you are unlikely to charge beyond 80%-90% of full capacity. In other words, a 10 Ah battery will provide 3-4 Ah usable power unless you abuse it. This makes a volt meter a really good idea but won't help if you're sleeping. Consider a Low Voltage Disconnect circuit such as this ST-BD01Q Seco-Larm Low-Voltage Battery Cutoff 12/24VDC Selectable
if you expect to get the rated life from your batteries (perhaps 200-400 charge cycles).
Understanding this makes LiFePO4 technology much
more attractive and affordable. Besides being much lighter weight, and the fact that they aren't at all unhappy with being discharged to 10% capacity, one can get similar performance from a battery with 1/3 the rated Ah with life expectancies of greater than 2000 charge cycles. Here is an example of the latest technology. 12V 12Ah, StarkPower 'UltraEnergy" Lithium Ion Battery (LiFePO) Energy Storage Battery
Not to mention that you won't be carrying an acid brick that might end up in the bottom of the river. They won't stay sealed forever.