Auxilary Battery systems


Well-Known Member
I am not the author of this article but it is interesting how sensitive some systems are, on our recent trip across the Simpson Desert a repeating problem occured in the Discoveries in our party, every now and again their electronics would spit the dummy by just running a car fridge.


According to a leading manufacturer of multiple battery control systems, premature battery failure is on the increase, "BUT DON’T BLAME THE BATTERY. The major cause of auxiliary battery failure is excessive sulphation.
Sulphation builds up on the battery plates during the discharge cycle of the auxiliary battery and is broken down by the alternator applied voltage and current, when the battery is recharged. Continuous discharging of the auxiliary battery below 11 volts may shorten the life of the auxiliary battery by as much as 20%."
"Auxiliary accessory equipment, ie fridge etc are not to discharge the auxiliary battery below 11 volts" .
Not only is the battery life affected, but the time required by the alternator to recharge the auxiliary battery is longer and in some situations with late model 4WDs (direct sense alternator regulator charge systems), may not recharge at all, as the alternator regulator will sense the over discharged auxiliary battery as a fully recharged auxiliary battery.
"Winches can cause problems too"
Alternators on late model 4x4s are not designed to support the high winch currents and may cause excessive over-heating of the alternator. Damage caused by alternator overloads due to accessory equipment is not covered by the vehicle warranty.
If the winch is connected to the main battery and the winch is turned off, high voltage spikes are
discharged throughout the vehicle’s electrical circuits and could damage sensitive computer circuits in the vehicle.
Recommend fitting an auxiliary battery, to connect and operate the winch. Also install a charge / isolator to charge the auxiliary batter. The charge / isolator design includes Assisted Alternator Protection, to isolate the auxiliary battery and the winch from the alternator and the vehicle electrical circuits, when the winch is operated. The alternator will be protected from the winch current overloads.
"Solenoids may be cheap, but they do not provide assisted alternator protection and they in themselves, unless suppressed, introduce high voltage spikes when turned off."
Solenoids also introduced voltage drop reducing the ability of the auxiliary battery to fully recharge.
The charge / isolator design ensures the high voltage spikes from the winch are reduced to a safe level and isolated from the vehicle electrical circuits, before the alternator is reconnected to the auxiliary battery for recharging.



I've killed my share of Deep Cycle Batteries in camper trailers, over the years. The problem is leaving them sit there, as you state "Sulphating". I fitted a Megapulse unit to my current Deep Cycle Battery 3 years ago, it is still fine (touch wood). Once a month, I put it on trickle charge for a day. The Megapulse has certainly paid for itself in the cost of replacement batteries. Check out this link to see how it works.
Megapulse First Aid Solutions



Active Member
What model Discos were they series 1 or series 2 or series 3 Discos:confused:

Series 2 Discos will boil a lead acid battery, due too the current output of the alternator, the auxcillary or starter battery needs to be an AGM, GEL or Calcium battery too except the charge rate the alternator puts out, series 3 Discos need a specific duel battery controller otherwise the electrics will play up.

I found this out the hard way as have with Disco 2 and Disco3 owners.

Since fitting an AGM as my auxcillary battery, i've had no problems, i also run a Traxide SC40 dual battery controller WITH THIS SETUP

the Disco 3 needs this kit in the link below too run an auxcillary battery

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