Recharging a battery

[Surfer]

Currently we have a newish Numax 110ah battery plus a 120w solar panel with a MPPT controller. We are away off grid for 5 nights and this is our first time off grid. If our battery goes flat and switches off the caravan's 12v taking into consideration the solar panel, could we hook up a second 12v 85ah battery using jump leads? The concern is if we remove the current 110ah battery, it can't charge up.
I was thinking more in terms of using the second battery so that we can go about our normal business in the caravan, but when we go out for the day, the solar panel charges the original battery or we can leave the second battery connected.
As totally noobie to off grid, we would like some advice as the wife is very keen on the TV which is 25w plus Sky 45w digibox although I may be able to leave the latter behind. it has taken me awhile to persuade her to go off grid and this was oen of her conditions. Thanks.

 

[Damian]

It is not sensible to connect two batteries of different ratings as they will try and equalise.
If you need two batteries it is best to have two identical batteries ,even then if one is slightly different, the two will try to equalise, usually at the detriment of the better battery.

Also at this time of year don't expect anything like the stated rating of the solar panel, you will be lucky to get even 20% of it due to the short hours sun and low trajectory of the sun.

 

[Surfer]

It is not sensible to connect two batteries of different ratings as they will try and equalise.
If you need two batteries it is best to have two identical batteries ,even then if one is slightly different, the two will try to equalise, usually at the detriment of the better battery.

Also at this time of year don't expect anything like the stated rating of the solar panel, you will be lucky to get even 20% of it due to the short hours sun and low trajectory of the sun.

Perhaps it is better to purchase another 85ah or 110ah battery and then to use this to run the TV and Digibox only through an 350w inverter? It has been suggested that we could then leave the 85ah battery in the vehicle charging it up as we drive around using a split charge wiring. This saves us lugging the battery in and out of the vehicle.

 

[Damian]

Everything you add to the electric usage will shorten the useful time of the battery.
Inverters are known to be not very good at converting 12v to 240v and as soon as the battery gets to a certain level , they will cut out
Going off hookup means making power savings, and depending on the items in your van it could be using a valuable amount of battery power, without adding TV, Digibox and Inverter.

If you want all the "bells and whistles" you will probably regret trying to go Off Grid, simply because they will not all work for very long.

 

[Gabsgrandad]

We spent many years rallying off hook up, in the days before solar panels were used on caravans. We’ve done as long as three weeks without mains and with 2 children with you it takes a bit! Our system was to take an extra battery and it was not connected via the van battery, but it was fitted with a socket (like the back of the car and wired to the permanent live pin) so the caravan towing lead was then plugged into this socket and the van electrics selected to car. We used to run off this battery mainly as we could each time we went out in the car it used to be secured in the boot and connected to the towing socket again so it charged up again. Also we used to use the car battery as well for the odd hour or two, again as it is charged up again each time you use the car. In fact we very rarely used the van battery as by the method we used, we kept it so that we always had power, for the van services from it. This system worked fine for us, just takes a little managing and thought on switching batteries. Never ran out of battery power, the secret is not to run any of the batteries too far down before switching and charging, obviously the car one, but there is a useful hour or two from it. Some other friends used to run a spare battery and rotate the usage and find a local garage to drop the discharged battery in for charging, a bit of effort but you don’t “get owt for nowt””!