Four basic ways to charge a lead acid battery.
1) Constant voltage around 13.4 volt for a 12 volt battery, used where battery is a stand-by.
2) Average charge often 0.5A at around 14 volt, with instructions not to charge more than 14 hours, often found with things like hedge cutters.
3) Stage charger, typical start at 3.8A dropping to 3A, then 0.8A and then 0.1A sold by Lidi and ctek MXS 3.8 as an example, plug in and forget.
4) Pulse charger, used a lot with solar panels, designed where the battery is used at same time as being charged.
Some units are very poor, a valve regulated lead acid (VRLA) should last around 7 years, but intruder alarms, stair lifts etc often have such a poor charger lucky to get 2 years out of the battery.
Some units, like the power packs made to jump start cars are supplied with a charger which can be left connected for years, but the battery that is used as it is charged is the hard one, simply adjusting voltage between 13.2 and 13.8 according to normal load you can get away with using and charging at the same time. However where charging time is limited, as with solar panels, you want to bang in as much as possible in a short time, So charger uses pulses, and it measures the decay time to adjust pulse size, also used with narrow boats.
With a fork lift, mobility scooter, milk float, then speed is important but battery is not used at same time as being charged, so three stages, constant current until set voltage, then constant voltage quite high around 14.8 volt for a 12 volt battery, but current is measured and once it drops to set level the voltage is reduced to around 13.6 volt. So 80% of charge is very quick, and last 20% is slow.
For a 7 Ah battery I use one of these
set to under 14 Ah it charges at 0.8A to start with, then 0.1A to finish off. With over 14 Ah it goes to 3.8A. However it requires the "MODE" button to be pressed, so depends what you are using the battery for.