In some cases pretty quickly over a week or so.  With extra electronics such as remote start, or say the computer in the boot of my wheelchair adapted minivan that controls the ramp, electric doors, suspension lowering and more the battery has double the drain on it while I get out and then again whilst it is sat unused on my drive! 

This damages ordinary car starter batteries quite fast through sulphation even if there is enough energy left to start the engine most of the time. So you will not necessarily know anything is wrong. Your battery will just suffer an early expiry.   See All about powerchair & vehicle batteries for more info.

Every time you switch off and get out, the ramp and suspension lowering (on my car for E.G.) as well as the door opening and closing motors all use lots of power. Your battery is already in a slightly discharged condition after you just exit it after a long drive. Batteries store or age well in a fully charged state. But they all sulphate internally if left in even a slightly discharged state for very long. In a relatively short time the batteries capacity or starting capability is then reduced.

Compounded by the fact that all those electrical systems mentioned above are still gradually taking even more power out, over time, as it sits there on your driveway. 

So if you leave your car or van for more than a week its a good idea to charge it. Or more accurately to "maintain" it in a healthy fully charged state. Your battery will stay healthy longer.

Buy a battery optimiser or battery maintainer as soon as possible if this scenario sounds like you!

Your battery will love you and it will stay healthy much longer. It doesn't actually need a full charge (although that wont hurt) but it needs a maintenance charger like this Optimate at the top of the page (or something similar) connecting and leaving connected while you are not regularly using your car.

It may well still start if you don't bother but your battery is suffering and will, sooner or later, let you down. Another alternative is a good solar charger of 2 to 5 watts. It wont "charge" your battery but it will keep it topped up hopefully and prevent it going flat and sulphating. Less than 2 watts is a complete waste of time unless you live in Arizona!  I leave a 5 watt one above plugged into the cigarette lighter socket and sat on my dashboard when I am not using my van. It keeps my battery fully charged up and healthy if the vehicle is unused for long periods. of a week or more!

See larger image of the Hawker Odyssey battery under test. 

Here is an example:

My Disabled adapted Rollx van. Has all kinds of immobilisers, satellite navigation, engine management, alarm and an extra computer in the boot to control the ramp/door/lowering etc.  Here it is with the vehicle all locked up and the engine stopped. After 30 mins. The Clamp Ammeter shows a 0.2 amp (200m/amp) drain on the battery. This is quite high but similar figures may be typical for some other modified vehicles of this kind.  20 to 50 m/amp is more normal.

2. Charging a powerchair or scooter battery:

Powerchairs and Scooters use Deep Cycle Batteries. These, despite their name, DO NOT LIKE  BEING DISCHARGED! All lead based batteries hate it, but deep cycle batteries suffer less damage when doing so.

With this in mind its best to ALWAYS charge them fully every single night in a powerchair or scooter if used at all during the day.  And once a week even if NOT used at all.  With the manufacturers charger or something equivalent with the correct charging profile for whatever batteries you have fitted.

A good Deep Cycle 3 or 4 stage logic controlled charger (switch mode or transformer) designed for the type of battery that you use is essential. Even if you only used your Power Chair or Scooter for ten minutes you must do a complete charge every night. Don't Forget. If you do and you continue to use it you will discharge your batteries much deeper than needed and no lead based batteries really like that. Regardless of what any "expert" may tell you!

REMEMBER!!! Charge weekly if you don't use it.   Nightly if you do use it.   Overnight.

If you have not used your powerchair or scooter at all then charge it once every week. Fully over night. Once a week will help prevent the batteries becoming slightly discharged and internally sulphated which ultimately is what kills them, if just left and allowed to become discharged. Never discharge Lead Acid Deep Cycle batteries on purpose to get rid of any memory effect!  They don't have a memory!  Even the original rumour that Ni-Cad batteries had a "memory" that came from NASA was not actually true in any normal use. All deep discharge does is damage your wheelchairs batteries faster.

If you get chance during the day it IS BENEFICIAL to plug in the charger to lower the average daily discharge level. This is called opportunity charging. Or opportunistic charging. Contrary to what you may read elsewhere by the less well informed it is definitely beneficial.  Anything that lowers the average discharge level each day helps your batteries live longer. It still needs the full overnight charge however every night just the same. The FULL charge cycle doesn't just "charge" but it also equalises all the cells in each battery bringing them all up to the same voltage level. So Plug it in for a while if you get chance while sat at a computer for watching TV.  But also do the full overnight charge too. Opportunistic charging does NOT replace it.

Are you fed up with waiting hours for your chair or scooter to charge? Well depending on your battery type you CAN fast charge them. I use Optima Deep Cycle and Starting batteries (Yellow Top ones) or Hawker Odyssey AGM batteries partly because it allows me to charge them up in the middle of the day up to a 95 percent full charge in around one hour. Go from all but exhausted, to ready to go again while you check your email... See here.  

It still needs the full overnight charge while you sleep from the normal slow 8 amp (or about 20 percent of battery capacity) charger however every night just the same or your batteries never get properly equalised and will become unbalanced.

Normal overnight (slow) charger size?  Its NOT at all critical unlike what some so called experts would tell you. The sizes below will get your heavily used scooter or powerchair fully charged and ready to go while you sleep. Smaller wont hurt the batteries at all. Even a 1 amp multi stage charger will safely charge your batteries. But it will take way too long!

3 amp for 25 amp hour batteries.
5 amp for 35 to 45 amp hour batteries.
7 to 8 amp for batteries 50 to 75 amp hour.

If you try to charge with a bigger charger but still of the correct multi stage deep cycle type then several things can happen.

(a) Depending on battery type you may have no problem at all. Your batteries will just charge faster. These chargers are voltage controlled so even a big charger will not hurt a good deep cycle battery unless it gets too hot. Too hot means about 50 degrees centigrade. I charge mine regularly at 30 amps.