When we changed our 110 amp battery to a Fogstar 105 amp lithium battery I was surprised how much smaller the battery was, we used the packaging supplied with the Fogstar battery to safely secure the battery.
The reason I suggested considering a smaller battery, was not for its physical size and weight (even though that could be a bonus) it was becasue if you are always using EHU, you don't use all the charge capacity of a big (and expensive) Leisure battery.
In fact with modern caravans (since about 1985) have been fitted with switch mode power supplies (SMPS) rather than simple battery chargers, and in fact with the exception of a caravan mover, in most cases you can safely run the caravan without a battery.
In the early years of SMPS's the manufacturers were a bit stingy and only fitted units with 8Amps output and some water pumps struggled to start, but these days most caravan supplies have 12 to 16A and again apart from the caravan mover these can handle all the caravans 12V needs without a battery!
Where a caravan mover is required, or they may be a need to have a permanent 12V feed for an alarm or volatile memories of radio's you may still need to fit a 12V battery of some kind. But contrary to the common perception caravan movers don't use a lot of energy (=kWh) and so they don't need a large caravan battery.
What caravan movers need is a battery that can deliver about 100Amps of current for a a second or two after which the movers current draw drops significantly as the motors spool up. Typical running currents of movers are in the low tens of Amps, it will only increase if the caravan is being moved up a hill or can't climb over an object, for example a tall kerb or stone.
When you look at the way a typical caravanner uses a motor mover its actual time running is likely to be less than 5 min. Even if it were 5Min that's only 1/12 of an hour which means it average current draw lets say 30A (15A a side) means it only consumes 2.5 Ah of the batteries capacity, and it would be typically less than that. Consequently most small car batteries are quite capable of this.
And of course once the caravan is sited and the EHU plugged in the battery will be recharged keeping it in good condition.
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