Dual Battery or Thumper

I have had a Thumper for years - dunno how many, maybe 8 or so - just starting to show signs of wear. Just put in an aux battery (AGM deep cycle) in the Cruiser, mainly to double the amount of battery power that I have available for both start and for running the fridge.

When they came out, Thumpers were tops - nowadays I would by an AGM battery and put it into a portable battery box. Reason - I think the AGMs are a better battery (get a good one though - cheap is not necessarily better) and 'cos the Thumper has dual batteries inside, if one goes it will drag the other one down. They are replaceable though.

Best, if you can afford it - aux battery AND a portable for running the camp site. Got heaps of power and a bit more flexibility.

viz

These 12v, 75 ah batteries are ~$700

ebay thumper link:Image Could Not Be Found
For that sort of money I think I would be using a much larger capacity AGM battery
place it in a basic battery box and add a few gauges
need to show at least Voltage and Amps going in/out
Battery cable, Anderson plug and Circuit breaker etc

Probably ~$450 with 100+ ah with 'quality' branded AGM battery

Maîneÿ . . .

Hi Zogs,
We bought a 48 amp hour thumper 6 years ago. The main reason we like it is it's portability. We use it to run a 12 volt versalight, an inverter with chargers for phones, ipods, cameras and a small fan for when I am having "moments" or a 12 volt camp shower that we usually set up away from our camper so as not to create too much mud. We have even brought it inside at home when there have been blackouts in storms to have light. The larger ones would be good but too heavy for me to lift and move around. Also have been tenting in national parks where koppers logs have been strategically placed inbetween where you park and where you are supposed to pitch the tent, so the portable one is good there too. They are fitted with cigarette lighter fitting and the stronger 12 volt one and heavy duty jumper leads and installation gear supplied. We don't run a car fridge so can't comment on that. We keep it topped up each day via car but I am sure solar panels could do the same if you were camped in one spot. Most important we have jump started a few deisels that have gone flat without compromising our vehicle electrical /computer system. The larger ones are better value. A dual battery system would have advantages too. But this set up suits us.
Cheers, Sally.

Zogs, I ended up getting a Thumper (60AHr) because there was no space under the bonnet to fit a second battery, so I really didn't have much choice!

Having said that, the portability of the Thumper is a plus, I just wish I'd gone a size bigger and got the 75AHr. I also found it tends to 'run down' abit even with driving a few hours every day - the charging circuit doesn't quite put in as much as the fridge is taking out. I'm currently looking at either an automatic switch-over (ie. fridge runs from car while driving and from battery while stopped, battery charges from car while driving) or a small solar system to 'top-up' the Thumper, particularly while stopped (ie. hiking, etc.)

IMHO a dual battery and a Thumper have different roles and a choice of one or the other is not simple.

For some years I have used one of the similar but smaller "Outback" units. Same manufacturer as the Thumper but only about 24ah. Some are 30ah. I think they may now market a newer version as "Urban".

This was in a car. I am now setting up my landcruiser trayback and there are some similarities to your situation.

What I like about the "Outback" is it is portable. It's good at jump starting vehicles without blowing electrics. It is not too heavy. I have looked at the Thumper and wonder whether it is really all that portable. I would not want to have to cart one too far. The "Outback" could easily run my fridge overnight in fridge mode. Freezer mode would be expecting too much. On the other hand I think a 75ah Thumper would be marginal for running a fridge/freezer. Freezer mode uses much more power. Perhaps 100-120ah would be more in line with your needs.

But doing it all again I would not have got the "Outback" for the car fridge. It really is best as a portable power pack. After all that is what it is. As a portable it is better in some ways than the luggable Thumper. Both are rather expensive though and there are some drawbacks.

Charging time is longer than for a dual battery under the bonnet. I suspect keeping the distance from the alternator to the battery short is good for reducing the charging time. With the Outback, and I think you would find a Thumper similar, to reduce charging time I had to run the fridge of one car socket and have the Outback plugged in to another socket doing nothing other than recharging itself. I never could get the "Outback" to fully charge if the fridge was plugged into it and turned on. Another writer has had similar experience.

After a while I got a a bit sick of having to disconnect the fridge from the car socket and plug it into the Outback each evening. I had the car sockets wired always on. In hindsight I would not do that again. It meant I had to be careful not to allow the fridge to flatten the car battery and being human this sometimes happened. So then I had to use the Outback to jump start the car.

It was all too fiddly. Now I would go dual battery if possible or if no space for a dual battery the best battery I could get would go under the bonnet. Possibly if space or carrying capacity allowed, a third battery would be carried as well and used for camp lights, jump starting or whatever. Probably the third battery would only rarely power the fridge. A Thumper could make an excellent third battery.

As I already have an "Outback" I will keep it in use. Got new batteries for it today. A recent jump start had sucked the last of the life out of the old batteries. but it won't be used for the fridge other than temporarily and then only overnight while travelling. A dual battery either under the bonnet or under the tray will cover that need eventually.

This response is a bit too long but I hope it helps a bit.

I am very greatfully for all your replies to this question and many others that I have asked. I think for this trip I will buy a branded 100ah Battery and box fitting 2x 12v outlets and 240v charger to recharge batt. when we do van park stops wich will be every third night, but if time pemits I might install a smart charger to start batt. with an Anderson plug to charge portable while travelling. Thanks again