Jud Chapin

For AGM starter batteries in both the C217 coupe and W222 sedan, WIS advises not to test it at the charging terminals under the hood due to possible faulty readings. This dictates that testing must be done directly at the battery terminals requiring removing trunk paneling. What a joke. Can anyone shed any light on this?

cyberay

Modern battery testers determine condition, at least partly, by measuring internal battery resistance where a difference of a few miliohms can result in pass or fail. Remote connections can have a small amount of external resistance between the battery and connection point which will be read by the tester as internal battery resistance and result in a fail indication. But there’s no reason an old-fashioned load tester can’t be used with a remote connection.