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ABOUT SEALED “MF” (Maintenance - Free) MOTORCYCLE / PWC BATTERIES
1) Maintenance-free "MF" motor-cycle batteries, also referred to as “AGM” (Absorbent Glass
Mat) batteries) or as “GRT” (Gas Recombination Technolo gy) batteries, are valve -
regulated and are constructed with glass-mat separators (to effectively absorb and retain
the acid electrolyte). They have important differences from "flooded" (with filler caps) &
other types of lead-acid batteries. These differences significantly affect the correct method
of charging "MF" motorcycle batteries. Automobile starter batteries marketed as
"Maintenance-Free" are not usually constructed with glass-mat separators, & should not
be charged on the BatteryMate’s “MF” charging selection.
2) The internal glass fibre separators leave less space for the battery acid than in
"conventional" batteries without these separators. The electrochemical nature of "MF"
batteries, is rather different from "other" lead-acid batteries as a result of these factors,
and they are not only more powerful than other batteries of similar dimensions, but also
retain starting power at very low temperatures far better than other batteries.
3) The dilute sulphuric acid electrolyte in motorcycle “MF” batteries is often more
concentrated (denser) than the battery acid sold at auto chains & service shops. For this
reason the acid for dry-charged “MF” batteries is delivered in a separate special pack with
the battery. “Wet” “MF” batteries are filled with special acid and charged at the factory.
4) To prepare dry-charged “MF” batteries, the acid must be allowed to trickle into the battery
at its own speed and the battery must then be allowed to stand for at least 20 minutes to
allow acid absorption & reaction before being sealed with the sealing cap strip provided.
Before being sealed any trapped air bubbles must be released by tapping the battery a
few times. The battery has now achieved about 70% of it’s full electrical capacity. Before a
new battery in this state is installed in the vehicle it should be brought to full charge on the
BatteryMate using the 'new’ battery setting (30 minutes). Such batteries have a kind of
memory effect in that if subjected to the full charge current from the vehicles’ charging
system before being given this pre-charge, the batteries tend to get “blocked” at about
75% of potential capacity thereafter. These “dry-charged” MF motorcycle batteries are
generally type-designated “YTX” or “YTL” or “YTH” if from Yuasa, with the “Y” replaced by
another letter if from another manufacturer.
5) “WET” valve -regulated MF motorcycle batteries are filled with acid and pre -charged by the
battery manufacturer. This has the advantage that the battery vendor or retailer does not
have to perform this task so the customer does not have to wait as is the case when dry-
charged batteries have to be prepared. Wet “MF” batteries have the disadvantage that the
self-discharge period is always greatly extended due to the transport distribution &
warehousing before the retailer gets to sell the battery to the user. It is therefore essential
for the vendor or retailer to re -charge these batteries before delivery to the user. In spite of
great recent improvement in the ability of batteries to retain their charge over time, due to
the prolonged interval between factory-commissioning of the battery & it’s sale to the user,
it is possible that the battery has already self-discharged significantly.
6) Fully charged “Dry-charged” MF batteries such as the YTX types should measure 13,15 V
across the terminals at 25°C. “WET” types of MF batteries typically have charged terminal
voltages around 12,85 V & flooded batteries around 12,65 V. Logically, the charging
voltage of dry-charged MF batteries therefore needs to be higher. The appropriate voltage
is not achievable with "conventional" vehicle battery chargers.
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