Leisure Battery Testing

Leisure Battery Testing

Introduction

This guide has been put together to help test and diagnose cases where a caravan or motorhome user is experiencing leisure batteries discharging or not lasting as long as expected and refers to electrical systems supplied by Sargent Electrical Services Ltd but may also be relevant to other makes or types.

From our experience, in nearly all cases of poor battery performance, a faulty or deficient battery (even a new one) is the cause of the problem. If two leisure batteries are fitted and one of them develops a problem, you will tend to find that the overall performance of both batteries is only that of the faulty battery.  With this in mind you should carry out battery tests on one battery at a time.

For calculation and testing purposes we are assuming a 110 Amp hour (Ah) AGM or wet battery is being used.  Most leisure batteries will only provide a usable capacity of about 80% of the stated capacity, so this is reduced to 88Ah.  Please be aware of this.

For caravans, consideration should be given to motor movers.  These units do place a considerable load (up to about 90A) on the leisure battery when being used.  It is important to ensure the leisure battery is rated for this type of current delivery, as many batteries may be damaged or their life drastically reduced if operated outside their design specification.

Prior to any testing there are a few things to do:
  1. Fully charge the leisure battery for at least 24 hours.
  2. Turn off the charger until starting any testing.
  3. Disconnect or cover your solar panel to ensure no readings are affected.
  4. Disconnect the Stinger alarm (if fitted).
The electrical control system in the caravan will draw a small amount of current from the battery to run the electronics.  This current is present by design and has been taken into account by the Sargent design team. Here is a list of typical current draw figures for common Sargent systems:

System
Power OFF
Power ON
EC400/450
100mA (0.1A)130mA (0.13A)
EC400+
60mA (0.06A)
90mA (0.09A)
EC600
70mA (0.07A)
200mA (0.2A) Screen On
90mA (0.09A) Screen Off
EC700
150mA (0.15A)
230mA (0.23A) Screen On
170mA (0.17A) Screen Off
EC800
150mA (0.15A)
230 mA (0.23A) Screen On
170mA (0.17A) Screen Off

Please note, if you have a vehicle battery connected then you may see a lower current as whichever battery has the higher voltage will provide the power for the control system. This is not to be confused with the power to the leisure loads - when the panel is turned on, these loads are drawn only from the battery selected via the control panel, and the leisure battery by default. 

Other items of equipment may also draw current on a permanent basis.  The Stinger alarm system will typically draw 4mA when the alarm is fully charged and operating, and can draw about 350 to 400mA when the battery is being charged.  This charging cycle lasts for about 30 hours and is triggered when a leisure battery is connected and the alarm battery is low.  The fridge, if turned on locally may draw up to 100mA (0.1A) depending upon model, switch off the fridge for testing.

Testing the PSU System

To measure battery charge / discharge current you need an ammeter connected in line with the battery feed.  This can easily and cheaply be achieved by using a plug-in meter (see the photo of an example below) that plugs into the leisure battery fuse location.  Alternatively, you can use a suitable multi-meter set to measure current, noting one with a 20A range is desirable.

To test the PSU system draw, fit the above meter or equivalent (as described above) in place of the leisure battery fuse.

With the PSU shutdown button out, record the reading on the meter, this should be zero.  If it is not zero then some other equipment which is not part of the original installation is connected and using current.  Please disconnect this equipment.

With the PSU shutdown button in, the meter should read approximately as per the list above in the Power OFF column.  As the meter being used is not a laboratory instrument the reading may vary slightly from that given above.

With the PSU shutdown button in turn on the control panel power button, the meter should read approximately as per the list above in the Power ON column, noting that all items should be turned off for this test and that the TV amp may draw a small current).

Now turn a few lights on and you will see the current reading increase.

Testing the battery charger

Following the above test, with the PSU shutdown button on (in) and the control panel power turned on, view the battery levels on your control panel.

Record the leisure battery voltage displayed on the control panel.  Alternatively, you can measure the battery voltage across the battery terminals with a volt meter.  This reflects the current leisure battery voltage and would be expected to be around the 12.7V mark.  As the battery has recently been on charge the voltage may still be higher for a while (say 13V to 13.5V) until the battery settles. Now turn the mains charger on, and you should see the voltage display rise. Again ass the battery has been charged, the charger should soon settle into float mode of 13.6V.

Now turn a few lights on and the battery voltage should change from 13.5V to 14.4V.
NOTE: Depending upon your control panel (e.g., EC400, EC400+) you have an LED display so you won’t get the exact readings given.

Testing the battery

Turn the control panel power on, and turn on some lights until you have about 5A shown on the ammeter.  This is going to be our discharge current.  Start a stopwatch or note the start time.

The battery will gradually start to discharge.  As the voltage decreases and reaches 10V the control panel will emit a warning and after a further period will switch the control panel power off.  Note the time on the stopwatch or work out how many hours have elapsed.

Now for the calculation, from a good 110Ah battery we would expect 88Ah, so at a discharge rate of 5A we would expect the battery to last for 17.6 hours (88 / 5).

Example; if the discharge rate on your test was 4.78A and the test lasted 13.3 hours, then the actual power delivered is 4.78 x 13.3 = 63.57Ah.

For a two-battery installation you should now swap the battery over, charge it fully as before and repeat the discharge test.  Both batteries should give a similar capacity if they are of the same type and rating.

If you do get a low reading it is worth repeating the test (time permitting) to see if you get the same result.

Poor batteries should be returned to the supplier or manufacturer for discharge testing and confirmation of your results.