There are a number of ways to charge a valve regulated lead acid battery.
1) Very low charge rate, designed to take over 16 hours, it does not show when fully charged and as long as voltage is OK then it does not matter if battery is 7 Ah, 70 Ah or 700 Ah it will just take longer often used to combat self discharge with larger batteries, cheap and nasty.
2) The stage charger, these are often split into three stages, max current, high voltage rapid charge, then finally a lower voltage equalising charge. It is the last function which means the charger has to be matched to a battery. With for example a 100 Ah battery the current will be set at around 2 amp, so it charges at 14.4 volt with valve regulated type, and once the current drops to 2 amp it drops the voltage to 13.2 volt to maintain the battery and bring it from 90% charged to 100% charged. Although much faster around the 10 to 12 hours to charge from fully discharged they have a problem, if you use the battery while being charged it can cause over charging.
3) The pulse charger, these measure the state of charge between each pulse, often called smart chargers, they both charge quicker and look after the battery better. Also they can be used with a higher range of Ah rating than other two.
So first thing is how long do you have to charge batteries? And are you prepared to change the batteries every couple of years? With VRLA you can't add water, so any over charging will destroy the battery. With a pulse charger they may last 10 years, with a trickle charger lucky to get 2 years. Some items like chair lifts will work for 6 years on a pair of batteries, but if left unused lucky to get 2 years as they are simply over charged.
At 7 Ah the battery is cheap, so if used say once every two or three days then the cheapest charger will likely do, but get a charger slightly too small rather than slightly too large. That will extend battery life.
But it is a trade off, the price of battery and how often it is replaced, to price of charger and with switch mode power supplies there is also a life, in the end the capacitors will fail and it will need replacing.
So mother hardly uses her scooter, I put it on charge for one day every month plus two days after she has used it. But wheel chair is used more, and it's important it can fully recharge over night so with latter a really good charger is required.