You can also shoot 'em with an IR thermocouple right down the fill cap. I had a mechanical thermometer with a monel probe that I loved but not as much as the @#$%^&! who loved it more. A pure glass precision glass thermometer will also work. Look for differentials. If the temp doesn't climb blast 'em with 14.8 until the cows moo. Five or ten thousandths of hard sulfated positive plate in the sediment chamber to render impressive performance for a few years is worth it. You'll know when you eee a decrease in charging voltage and increase in amperage your leechcraft is working.