I have never seen a lead-acid battery charged at only 50mA.
My tiny Ni-MH AAA cells charge slowly at 85mA.
I have float charging lead-acid batteries for years. Take my airplane. It has a flooded-cell lead-acid 12V battery. The voltage regulator/60A alternator does a great job of charging the battery (VR is set to 14.25V +- 0.1V for temperature compensation).
Upon returning from a several hour flight, the state of charge of the battery as determined by using an accurate hydrometer is 90% to 100%. The airplane is hangared and sometimes sits for up to three or four weeks before being flown again.
I use a 2A regulated float charger set to 13.10V (winter) and 12.90V (summer). The current is metered. If I plug it in after a flight, the current is zero because the battery voltage is higher than the charger voltage. There is a diode in the charger so that the battery cannot discharge into the charger. It takes ~24 hours before the battery voltage to fall off before any current flows into the battery.
Initially, the current is small, a few mA, and then over the several hours, the current asymptotically settles to a steady-state current which just matches the self-discharge current of the battery. Here is what I see:
Newish 35Ah FLA battery: 50mA
4 year old 35Ah FLA: >120mA, which means replacement soon.
newish 55Ah FLA: 70mA
4 YO 55Ah FLA: 150mA
Newish 100Ah SLA:20mA
five y.o. 100Ah SLA:75-90mA
These depend on ambient temp. The self-discharge rate of all lead batteries is much higher at 85degF than at 45degF.
In the case of the solar charger, it too is metered, and the current drawn by the floated batteries is similar.
Another data point. If I forget to plug in the float charger after a flight, and the airplane sits for say a week, and then I plug it in, here is what happens:
The battery has been self-discharging for a week, during which it has lost some small fraction of its total charge, maybe 1-2%. If I measure the open-circuit battery voltage before plugging in the charger, I would see about 12.60 to 12.65V (depends a little on ambient temp and the age of the battery). When I plug in the charger, it pegs the ammeter at 2A. It takes about 15min for the charging current to begin to taper. It takes several more hours for the current to asymptotically settle to the same steady-state float current as described above; it just approaches the asymptote from the other side.
Now, without float charging, a FLA battery will loose 3-5% of its charge (as measured with a hydrometer) in a month at 70degF. Up to 10% of its charge per month at 100degF (1-2% per month at 40degF). Before I began using a solar float charger, in three months during hot weather (Utah/Arizona border in the red rock desert), the starting battery in the boat would not crank the V8 long enough for the fuel pump to refill the carb bowl (all the fuel evaporates in three months), because it had lost so much of its charge due to self-discharge. Floating fixes that.
It also fixes another problem. If a FLA (or SLA) is allowed to sit with less than about 90% SoC, it grows a hard form of lead sulphate, which don't dissolve. This reduces plate area, and reduces the Cranking Amp Capacity of the battery. The only way to prevent hard sulphates from forming, is to maintain the battery at a SoC >90%. Floating does that because the charge that otherwise would be lost to self-discharge is replaced in real time. Before floating, I was replacing my boat batteries every two years. With the solar charger, I'm getting 4 to 5 years per battery. Note that this is comparable to what you get out of a FLA in a car that is driven daily...
btw- I have been boating on Lake Powell since 1973. I have stored a boat there (in dry storage) for >25 years. I have had various incarnations of the solar charger running there for about 15 years. There is no AC power available where the boat is stored.
ps: This is why I have been boating on Lake Powell for almost 40 years: