Ktmrfs
KUDOS for being a authentic GREEN minded individual.
Batteries that do not BUBBLE are batteries at risk. Not Old Faithful grade bubbling or Bikini Atoll H-bomb test bubbling but slight bubbling in every last cell. This is an excellent way to tell if your cycled batteries are being recharged correctly. Then use a hydrometer. Meters help.
Most of today's converters deliberately undercharge a battery to prevent the manufacturer from ending up in court being sued for boiling dry a battery. The new new converters are designed to protect know-it-all owners with double digit IQs. Plugger in and head for the brewskies.