a one amp charger will work but since it is only a trickle charger - leave it on for at least 24 hours. It is a good investment to get an automatic charger that shuts off when the battery is fully charged. They usually come as a 10 amp fully automatic or a 10amp - 2 amp with a switch fully automatic charger. They run about $35-50. Great investment as if you forget to turn a manual charger off because you got busy doing something else - you won't damage the battery. JDUB had an excellent idea about checking the level of electrolyte first. Up here in cold country it is not a problem, but if you are in an area that is hot a large portion of the year - the elecrolyte will evaporate and lessen the capacity of the battery even causing the plates to warp and destroying the battery. No matter what make of car you own - a cheap digital multimeter and an automatic battery charger are very essential DIY tools. Makes problems like yours a snap to fix.