Different batteries require different charging profiles and voltages – if you want to get the most out of an AGM battery then you should ideally use a DC-DC charger as well as a solar panel to ensure that your second battery is getting charged properly while you drive and while you’re at camp. A DCDC charger combines a battery isolator, with an multi-stage battery charger (not just a constant alternator charge) plus they are able to charge different types of deep cycle batteries with different chemistry like AGM batteries – which require a higher charging voltage. DCDC chargers are perfectly suited to smart or eco type alternators and some models like the Adventure Kings 25A DC-DC Charger Mk2 have a separate solar input too!

They work by taking the input voltage from the starter battery, and boosting it up to the required voltage to perfectly charge your auxiliary battery. So whether you’re trying to charge an AGM battery from an old alternator that’s putting out 14V or a temperature compensating alternator that has dropped right down to 13V, the DCDC charger will still be able to provide the 14.6V that your second battery requires. There’s a couple of other benefits too, a DCDC is capable of recognising deeply discharged second battery that is right down to 5 volts and will charge them back up. So long as the deep cycle battery isn’t permanently damaged it will revive it! DCDC chargers directly monitor the auxiliary battery voltage and state of charge and then varies the voltage and amps that it’s charging, not just a constant charge like a VSR or isolator switch provides. It’s reading the auxiliary battery’s temperature and adjusting its charging to suit – pushing too many amps into a battery causes them to heat up quickly and heat is the biggest killer of AGM batteries. Because it’s at the end of the wire run, even if there’s voltage drop in the wiring, a DCDC charger will still provide the correct voltage to the second battery.

For the same reason they’re perfectly suited to a temperature compensating alternators or smart alternators – not only will it boost the voltage up as required, but the Kings DCDC charger Mk2 has an ignition sense wire that when connected to an ignition source tells the DCDC charger to start charging the second battery. That means that even with the smart alternator turning off and not charging, the DCDC charger will continue – that in turn will drain your starter battery over time and cause the alternator to turn back on! That means you’re still able to save fuel, without over draining your auxiliary battery. If the blue wire wasn’t connected, the smart alternator turning off would make the DC charger isolate the batteries – and not reconnect til the alternator started up again. The blue ignition sense wire on a Kings DCDC charger makes basically any charging system better – modern vehicles with smart alternators, long cable runs powering house batteries in trailers or caravans and even older vehicles with basic alternators – particularly those that suffer voltage drop when you flick on the headlights and windscreen wipers.

The next awesome function is the solar input – this is available on this Adventure Kings 25A DC DC charger and is connected to the built in MPPT solar controller to ensure your second battery always receives the right amount of charge. MPPT or maximum power point tracking is a hugely efficient and powerful system for making the most of your solar panels – like its name it’s able to find the maximum power point and constantly varies the volts and amps to provide the most watts from your panels into your batteries. In the Kings 25A DC-DC model the solar is prioritised over the alternator input – it’ll always use solar power first, then top up the rest with the alternator to constantly keep your auxiliary battery topped up – it will use the solar input right up to the full 25A if it’s available from your panels!

When you’re shopping for a DCDC Charger you want to look for a model that’s able to put out the stated amps even when it’s working hard or heating up – for example the Kings 25Amp DC Charger is able to put out 25A even when internal temperatures are approaching 100°C. Of course it also features that auxiliary battery temperature sensor, so it’s been designed so the battery is the limiting factor – because batteries shouldn’t be charged over 50°C, a quality DCDC charger will taper off the charging if your deep cycle battery starts warming up too much – again that’s the advantage over a more traditional dual battery setup.

At the end of the day your dual battery system can be built in a number of ways, but an Adventure Kings DCDC charger combines a lot of the features you need into the one unit – it’ll always charge your auxiliary deep cycle battery more precisely than a basic system and they give you the option of plugging solar directly in too. They’re almost a necessity if you’re running batteries that require different charging voltages –such as the Adventure Kings AGM deep cycle battery – and in many setups that’s the case – whether it’s due to the battery chemistry needing a higher voltage than your alternator can provide, or whether the battery location means that voltage drop will make charging inefficient, they’re also particularly important if you’ve got a smart or temperature compensating alternator.

All in all do your research and decide which setup is right for you – whether it’s a separate deep cycle battery in a battery box that you charge with solar and top up at home every time you use it, or a completely permanent, multipurpose DCDC charger that means you never even need to think about your auxiliary battery, you just know it’ll charged properly every time whether you’re driving or connecting your solar panel directly.