|The batteries specified for the M201
24 volt are two 45 amp-hour type. The un-rebuilt jeep in the
photo opposite is M201 no. 25874 with everything under the
bonnet pretty much as it left the factory apart from the
liberal waxing it received before going into storage at some
point. Batteries were removed from jeeps to be sold at
auction ( a French regulation) and are obviously not the
original item but are ex-French army NOS which bizarrely
were actually sold at auction.
The batteries shown are the 45
amp-hour size made for the army by VARTA in Germany.
Note also the quick release
An important point to make at this stage is
that the batteries should always be replaced as a pair with
the same capacity and from the same manufacturer
otherwise charging will not be equal and battery life will be
My personal quest for authenticity with my
jeeps does not, however, run to batteries! The main reasons are the
cost of 45 amp-hour batteries, two at a time, together with the fact
that lack of daily use during the summer and a long period of
inactive storage over the winter is not good in terms of battery
life expectancy. The principal culprit is something called
'sulphating', the build-up of a layer of lead sulphate on the
negative plates that occurs
where a lead-acid battery is not kept fully charged.
This reduces the capacity of the battery to hold charge, increases
the internal resistance and ultimately the battery cannot deliver
the 'umph' required to start the engine however long you charge it
for. I use the cheapest batteries I can get that will fit, usually
038 type intended for Rover Minis and the like. They are a bit
small for the frames that hold them down but with a bit of packing
all is fine and unless you are using a radio transmitter there is
little if any need for 45 amp hour capacity.
|To measure the amount of charge in a
lead-acid battery accurately really requires measuring the
specific gravity of the electrolyte using a hydrometer.
These are still available though of course most modern
batteries are 'sealed for life'. In any case using a
hygrometer is a tricky business which can lead to acid
getting on things it shouldn't. The voltage of a lead-acid
battery can be used as a pretty good guide to the level of
charge provided it has been idle for at least 8 hours with
no load attached (isolator
off). (note the table is for one 12 volt
The evil process of
sulphating begins to occur whenever the battery voltage
falls below 12.4 volts or about 70% charge. The rate of
sulphation increases dramatically with further falling
charge level. The simplest and cheapest way of keeping it to
a minimum is to ensure that the batteries are kept fully
charged as possible which is particularly important if the
jeep is laid up over the winter period. There are
anti-sulphating additives available and special electronic
chargers that produce a pulsed charge that can even reverse
the effects of sulphation but keeping a full charge is the
simplest and most cost-effective.
BCI Standard figures
these readings are for standard batteries. 'Calcium'
type batteries will be 5 - 8% higher
Unlike a 'leisure battery', an
automotive battery is not designed for what is called 'deep
cycling'. It can withstand the occasional drop into the
yellow zone provided it isn't left there for long but
allowing it to go flat before recharging will reduce its
life significantly and leaving it flat for some time may
even end its operational life.
When the two 12 volt lead acid batteries in an
M201 are being charged the voltage rises to between 28 and 29 volts,
any higher than this and the batteries will be seriously damaged.
One function of the regulator is to ensure that this does not
happen, its full function is described on the
regulator page. The exact setting
is a compromise and is dependent on the temperature range that the
jeep is likely to have to operate in. The factory setting was a
nominal 28 volts, perhaps not surprising given the need for desert
Maximum service life; the battery remains cool during
charge; the vehicle can operate in temperatures
Faster charge times and the battery is less likely to
suffer from sulphation.
Slow rate of charge and sulphation of the negative
plates will occur if the battery is not regularly given
a top-up charge.
Battery will be seriously over charged at temperatures
>30°C and 'wear' of the positive plates (known as
corrosion) is increased.
GOOD PRACTICE TO PROLONG BATTERY LIFE
- Replace batteries as a matched pair and
avoid using one battery to power 12 volt accessories, camping
- Check the state of charge regularly and
charge the batteries if this falls below 75%. This is
particularly important if the jeep is laid up for the winter.
- If the battery does go flat then charge
it up as soon as possible. The run home from a show is unlikely
to be far enough to fully recharge the batteries.
- Check the voltage regulation - it should
be between 27.5 and 28.5 volts. If it is outside this range the
regulator certainly needs
Bubbling or 'gassing' becomes quite vigorous
as the battery nears full charge if you are using a traditional type
of battery charger. It requires a period of time like this for the
batteries to actually reach 100% charge.
Most batteries these days are classed 'low
maintenance' and do not require 'topping up'. When they do it is
usually a sign that they are pretty much time expired. If your
battery is fairly new and requires this then the chances are that
the batteries and being over-charged and the
regulator requires attention.
A fairly new battery put away for the winter
fully charged should hold its charge till the next season but as a
battery gets older it will tend to slowly self-discharge and will
need a top-up charge from time to time.