Yes, I've see that.
A couple of good points raised about which type of battery to use and if they should be identical. This comes up in a lot of the topics about the Traxide and the way it keeps the batteries linked until the voltage has dropped off further than most split charge systems. Point to note, it disconnects at 12.0v and reconnects when the main battery is back up to 13.2v.
At 12.0v, most batteries are no less than around 70 or even 60% discharged and will still have most, if not all of their cca capability.
Once disconnected at 12.0v, assuming there's a load on it just before disconnection, the battery voltage will actually recover slightly, possibly up to around 12.4 or 12.5v, and assuming no further discharge load is applied (or very minimal load - a couple of ECUs, a tracker and an alarm system with a warning light), the battery is in good condition, and it's not freezing cold, it will remain there for a good many hours, days, in fact. How often do you leave a vehicle parked for days, or even weeks, and the battery still has enough to get the engine started.
In my post about balanced battery charging, the batteries should be identical as well as having identical length connecting leads to get the best out of the system and prolong battery life as much as possible.
Cranking batteries are best run with only minimal discharge regularly, leisure batteries are best if heavily discharged, or deep cycled regularly. The other things to consider are that a so called cranking battery will deplete quickly, if discharged too much (below around 60 or 50%), but will still produce a voltage all the way down, whereas a leisure battery will hold a decent voltage for longer, but will suddenly drop right off, rather than hold it's voltage, below a certain threshold (normally around 50%).
For the Traxide to get the best out of both cranking and auxiliary batteries then, they should be the same type of battery, but be capable of cranking (high cca) and leisure (deep cycle).
So, a dual purpose battery is required (either AGM or lead acid) for this to work. What we're after here is the right combination: decent Ahr (110 - 150 maybe - depends on individual builds) for deep cycling, but a decent cca for starting (here I'm thinking in excess of at least 1000 cca, to get that sluggish, old and grumpy oil burner woken up when it's way too cold to be happy).
If my thought process is right, my next battery purchase is going to be 3 AGM or lead acid dual purpose batteries (one for cranking, and two for auxiliary) with around 110 - 150ahr capacity and 1000 to 1200 cca each. Then install the Traxide (or similar), with solar and shore power etc...
That way, I have the ability to start after it's been stood for a while, run front and rear winches (hopefully not at the same time
), run the fridge/freezer and other auxiliary equipment for hours without the need to recharge and, if the main battery does fail, swap it out for one of the auxiliary batteries because they are all the same and I'll still be left with a powerful (reduced capacity) split system.
