Battery run time is the specification most often quoted in a way that cannot be reproduced on site. A machine advertised at five hours that manages three is not usually faulty. It is usually being measured differently.
Ask what was running
A scrubber dryer draws current from four places: the traction motor, the brush motor, the vacuum motor and the solution pump. The brush motor is the largest single draw, and it rises with brush pressure. A run time measured with the deck raised and the vacuum off can be nearly double the real figure.
The question to ask is simple: is this run time with the deck down at working pressure and the vacuum running? If the answer is anything other than yes, the number is not a working figure.
Capacity is not the whole story
Amp hours only compare directly within the same chemistry. A lead-acid battery should not be discharged much below half its capacity without shortening its life badly, so a 200 Ah lead-acid pack has roughly 100 Ah of usable energy. A lithium pack of the same nominal capacity can be taken far deeper, and it holds its voltage as it discharges, so the machine does not slow down towards the end of the shift.
That is why a 100 Ah lithium pack often outworks a 150 Ah lead-acid one, and why comparing the two on the label is misleading.
Charging is part of the plan
Lead-acid needs a full uninterrupted charge and a cool-down before it goes back to work, which in practice means one machine, one shift, one charge. Lithium accepts opportunity charging: half an hour on the charger during a break puts real working time back into the pack without damaging it.
If your building is cleaned in two shifts, opportunity charging can be the difference between one machine and two. That is a bigger number than any price difference between the packs.
What to specify
Work out how long the machine actually has to run between realistic charging opportunities, add 25 per cent, and specify against that. Then check the charger: input voltage, single or three phase, and whether the charging point is anywhere near where the machine is parked. A pack that cannot be charged where the machine lives will not be charged.
Two things to check on site
Look at where the machine is stored. If the charging point is on the far side of the building from the machine park, the pack will be run flat and left, whatever the procedure says. And check the ventilation requirement: lead-acid batteries give off gas while charging and need a ventilated charging area, while lithium packs do not, which sometimes decides the question on its own in a building with no suitable room to spare.
