If cared for well, batteries can last for well over 3 years. However, misuse can reduce their life to a year or less. Put simply, lead acid batteries like to be charged all the time and not left discharged.
A faulty battery can cause the instrument to lose contact with the PC or just not work at all.
To test the battery, leave the instrument on charge for and hour or so and then leave off charge for a few minutes. Examine the field machine car battery connection, you will see four pins, measure the potential between the top pin and either pin to the left or right. The potential measured should be around 12v. Turn the instrument on and see that the potential does not reduce by a great amount. Connect the mains supply, so the instrument starts to charge and the potential measured should increase up to about 13.7vdc. If any of these potentials look wrong, contact ACM Instruments for advice.
Caring for your battery: