Floor Machine Battery Selection
Floor Machine Battery Selection


I just want a good battery – how do I choose?

In order to make an informed battery buying decision, you need to understand some fundamental differences in the way batteries are constructed. These differences result in performance advantages that will be more or less important to you. The parameters may be cleanliness, ease of use, run time, initial cost, environmental factors, hazardous gases causing explosion hazards, and other criteria.

Wet batteries consist of lead plates mounted in a liquid sulfuric acid solution. Due to their internal chemical reactions and heating during charging, they inherently lose water that must be replaced through regular maintenance, or damage to the batteries will occur.

Gel and AGM batteries belong to a family of batteries called VRLA, or Valve Regulated Lead Acid. They are sealed and do not lose water during charging, and therefore are referred to as being “maintenance free.” Although wet and VRLA batteries are similar in key design fundamentals (a lead surface and a sulfuric acid electrolyte), they differ in construction and application.

Wet / Flooded Batteries


  • They have the lowest cost for a given runtime/amp hour
  • They tend to have the longest life span if properly maintained and not abused.
  • Most use Lead-Antimony plates, which have improved plate strength, an important feature for electrical vehicles that are subject to abrupt stops and starts, bumps, and vibration.
  • They can tolerate frequent charge/discharge cycles


  • Lead-Antimony plates, although stronger than the Lead-Calcium plates used in VRLA batteries, inherently have a much higher self-discharge rate. This means that wet batteries cannot be stored for any length of time without supplemental charging to make sure the plates do not sit in a discharged state, which will allow sulfation, battery degradation, and premature battery failure.
  • Care must be taken while handling wet batteries so as not to expose personnel, other equipment, or delicate surfaces to sulfuric acid that may spill when the fill ports are uncapped or if the battery tips.
  • During the charge process, an explosive mixture of oxygen and hydrogen is produced that may accumulate in pockets outside the battery, so wet batteries need to be properly ventilated and are subject to shipping restrictions.
  • They must be kept in an upright position to prevent leaking and spilling
  • There are associated costs and inconveniences related to the required regular servicing needs of wet batteries, such as damaged and/or special clothing, hazardous material handling and transport requirements, shipping restrictions, damage to service areas from acid, and other personnel-related costs that should be considered when choosing a battery. However, by far the biggest cost is incurred by not maintaining the batteries.
  • Freezing – A fully discharged wet lead acid battery will freeze at temperatures close to -10°F. The expansion of the electrolyte can damage the plates, separators or even crack the battery case. If freezing should occur, you must let your battery thaw, physically inspect the case for leakage, fully recharge it in a well ventilated area, remove the surface charge, and load test the battery and charging system to determine if there is any latent or permanent damage.

Valve Regulated Lead Acid (VRLA) Batteries

  • Encompass both gelled electrolyte (gel) and absorbed glass mat (AGM) batteries.
  • Battery housing is sealed with pressure relief valves that typically cannot be modified or removed.
  • No maintenance – you do not add water to the cells.
  • According to industry experts, the shelf life of a VRLA battery is seven times higher than the shelf life of a comparable wet battery.

To avoid damaging your batteries, do not mix wet and VRLA batteries on the same machine!

Overcharging is especially harmful to VRLA batteries because it dries out the electrolyte by driving the oxygen and hydrogen out of the battery through the pressure relief valves, where it cannot be recovered. A battery can be overcharged even though it is not fully “charged”. That is why using the proper charger and charger algorithm is critical for battery performance.

Battery manufacturers consider the battery warranty void if improperly charged.

Gelled Electrolyte Batteries

Gelled batteries contain sulfuric acid that has been gelled by the addition of Silica gel, turning the acid into a solid mass the consistency of petroleum jelly that coats the lead plates.


  • Gelled batteries are sealed, have special pressure relief valves and should never be opened.
  • Since they require no maintenance, they don't have the costs and inconvenience of regular servicing associated with wet batteries.
  • It is impossible to spill acid even if the battery case is broken; therefore it can be operated in virtually any position other than upside down.
  • They are very safe at sea - no chlorine gas can form due to sulfuric acid and salt water mixing.
  • Gelled batteries can be stored at sub-freezing temperatures as low as -25° to -35°F, as long as they are fully charged prior to storage.
  • Gelled batteries use a recombination reaction to prevent the escape of hydrogen and oxygen gases that are normally lost in wet batteries under normal operating conditions. However, the batteries should still be ventilated.
  • Because of their “acid-starved” design, gelled batteries are better suited for deep-discharge applications that would otherwise damage the plates of wet or some standard AGM batteries (not the Discover AGM batteries offered by Nilfisk-Advance).
  • According to industry experts, the chance of explosions for gel batteries is as little as 1 in 1,000,000 compared with 1 in 1,000 for wet acid batteries.


  • Gel batteries must be charged at a slower rate to prevent excess gas from escaping and damaging the cells.
  • They must be charged at lower voltages than flooded or AGM. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity.
  • Although gel batteries are sealed, there is some water loss. In hot climates, water loss can be enough over 2-4 years to cause premature battery failure.
  • Their initial cost is higher than wet batteries for a similar amp hour capacity
  • They are heavier than comparable wet batteries.

AGM Batteries

Absorbed Glass Mat batteries utilize a very fine fiber Boron-Silicate glass mat between the plates. This mat can take more abuse than gel.


  • AGM batteries are sealed, have special pressure relief valves, and should never be opened.
  • Since they require no maintenance, they don't have the costs and inconvenience of regular servicing associated with wet batteries.
  • The sulfuric acid cannot spill, even if the battery is severely overcharged or broken, because it is contained in the glass mats
  • no chlorine gas can form due to sulfuric acid and salt water mixing.
  • AGM batteries can be stored at sub-freezing temperatures as low as -25° to -35°F, as long as they are fully charged prior to storage.
  • Most types are recombinant, where Oxygen and Hydrogen recombine inside the battery – this results in efficiency of over 99% and almost no water loss.
  • Internal resistance is extremely low, so there is almost no heating of the battery during the charging process.
  • AGM batteries have a very low self-discharge – from 1 – 3% per month, so they can sit without charging in storage for much longer periods without damage than wet batteries.
  • Since the lead plates are tightly packed and rigidly mounted, AGM batteries withstand shock and vibration.
  • AGM batteries excel for high-current, high-power applications and in extremely cold environments.
  • Compared with the same size gel battery, AGM's will have a higher amp hour rating and therefore deliver longer run times.
  • Classified as non-hazardous, thus their shipping costs are lower.
  • They don't have the maintenance costs associated with wet batteries.


  • AGM batteries cost 2 to 3 times as much as flooded batteries of the same capacity.
  • Where there is adequate ventilation and no leakage concerns, flooded batteries are a better economic choice.
  • AGM batteries can be susceptible to thermal runaway during charging because of their recombination reaction. This is another reason why it's so important to match batteries with the appropriate charger and algorithm.


Lead-acid batteries contain sulfuric acid, a highly corrosive poison that may produce explosive gasses when the battery is recharged. This can hurt you! Therefore, when charging or working with batteries:

  • Make sure they are well ventilated. If accessible, open the machine battery compartment cover or seat and leave it open during the charging process.
  • Remove your jewelry, wear safety goggles, protective gloves, and clothing.
  • Be careful with your tools so you don't drop a metal tool across exposed battery terminals – the resultant spark may cause an explosion.
  • Do not allow battery electrolyte to mix with salt water. Even small quantities of this combination will produce chlorine gas that can kill you.
  • Refer to the Charging Do's and Don'ts section for more instructions on charging specific battery types.