Originally Posted by TERRORTORY
hey guys i just bought a new territory ts great car just wondering if anyone knows were i can mount another battery in the engine bay so i can use it to power my uncles breathing pump when we go camping, i was thinking above the exaust near the coolant bottle, i dont wanna put it in the boot because i need al the sapce i can get
Batteries and heat don't go together - some are much better at being in a hot environment than others, but generally you would not be wanting to place the battery any closer to a heat source than is already the case with the standard battery location.
Other consideration is that if you intend to charge it via the vehicle's alternator, you will need some form of battery isolation system that recognises that you need to start and charge the primary battery before it switches current to the second battery - do not just parrallel up the batteries - grief will result, and your warranty will be cactus. Intelligent chargers that recognise when the primary battery is needed for starting, and needs charging (not simple relay systems that switch between the two batteries) are minimum $500, plus installation/wiring, plus you need a location for the 2nd battery, and wiring to wherever you will power your loads from.
My suggestion is: If powering the breathing pump is the only load on this 2nd battery, why not just have a separate battery - not mounted to, or connected to the car, you just pack it when camping - and charge it using a high-current petrol powered battery charger like the Christie unit - http://www.christieengineering.com.au/2.5hp.htm
This charger will fully charge a dead flat battery in about 1/2 an hour or less, top-ups are accomplished in 5 - 10 minutes. An Absorbed Glass Matt (AGM) battery is the best type to use with chargers that charge at this high rate.
As you will notice from the pics, it is just a 55 amp alternator coupled to a 50cc Honda engine, with some smarts thrown in to control over voltage in load dump situations, and a method to switch between high and low rates of charge.
I actually made my own version of this (same engine and alternator) which works really well. Unless you have an engineering background and just want to do it for fun (like I did) - I don't suggest you contemplate making it yourself. You won't save any money! There are cheaper units that do similar things - two stroke units that typically charge at 30 amps or less, but the Christie unit is a high quality product. If you go down the path of charging an external battery, don't fall into the trap of trying to use the 12V output on those cheap 240V generators sold by GMC and the like.
1. The 12V outputs on these generators are very poorly regulated;
2. You are unlikely to get more than 8 amps out of them;
3. The whole process will take wayyy longer;
4. The poorly regulated (if at all) output will have no way of increasing or decreasing the output as is needed by the battery as it charges; and
5. The output voltage is usually way too low - a battery needs to be charged by a voltage source greater than itself to charge. An alternator does this by typically charging at between 14.1 - 14.3 volts. The Christie unit can switch between a normal charge rate of 14.3V and a high rate of around 15.1V
Hope all this helps your decision.