What AGM battery suits an older fifth wheel with no solar or inverter?

Answered by RV Parts Giant · Upland, CA · September 27, 2026

Short answer: A sealed deep-cycle AGM sized so that half its rated capacity covers a night is the right answer for a rig that mostly sits on shore power. Buy on usable amp-hours rather than the number on the label, because lead-acid gives you about half of it, and make sure the converter is set to AGM with no equalise stage.

AGM is a reasonable choice for exactly this rig. It is sealed, so there is no watering and no vented box requirement, it can be mounted in any orientation, it charges faster than flooded, and it holds charge far better in storage. Against lithium it is heavier and shorter-lived, but without solar or an inverter you are not using the deep daily cycling that makes lithium pay.

Size it on usable capacity, not on the label

A 100 Ah lead-acid battery is a 50 Ah battery in practice. Take an AGM past about half discharge regularly and its cycle life falls away quickly, so plan on roughly 50 to 60 percent of rated capacity being usable.

Work out what a night actually costs you. Without an inverter, the loads are lights, the water pump, the fridge control board, the furnace fan and a few phone chargers — and the furnace fan is the big one in cold weather. A 100 Ah AGM comfortably covers an overnight stop between powered sites. Two 100 Ah batteries, or a single 200 Ah, covers a long weekend with the furnace running.

Typical figures for AGM are roughly 500 to 1,000 cycles at that depth and about 60 to 70 lb for a 100 Ah 12V battery. Those are ranges rather than a specification for any one product — check the datasheet for the battery you actually buy.

The setting that decides how long it lasts

AGM wants a lower absorption voltage than flooded, and no equalisation at all. Overcharging AGM dries the mats and kills it, and an old converter left on a flooded profile with a periodic equalise stage will do exactly that.

So check the converter. If it is a single-voltage unit or it has an equalise mode you cannot turn off, the battery will not reach its rated life no matter which one you buy. A configurable shore charger with a selectable AGM profile solves it, and costs less than the battery you would otherwise cook.

Two things worth adding, and one to skip

Add a shunt-based monitor if you ever park away from power. Lead-acid voltage under load is a poor indicator, and guessing is how batteries get taken to 20 percent and ruined.

Add a battery disconnect or use the existing one during storage. Parasitic draws from the propane detector and radio memory will flatten a bank over a winter, and a lead-acid battery left flat sulphates and does not come back.

Skip the upgrade to lithium for now if the rig genuinely stays on shore power. The case for lithium is built on deep daily cycling, fast alternator or solar charging, and weight — and you are not doing any of the three. If you later add solar or an inverter, revisit it then, because the charging side has to change with it.

Tell us your overnight loads and how long you stay off power, and we will size it. Everything ships from our warehouse in Upland, California.