;e important things to consider
when looking at any batteries,
whether NiMH or LiPo, are capacity (which
determines how long your car or truck will run per charge) and voltage
(which determines how much speed and power your model will deliver).
Here’s what you need to know:
;e big number on most battery labels (3300, 4000, 5000, etc.) indicates
its capacity in milliamp hours, which is generally shortened to “mAh.” ;e
greater the mAh number, the longer your car will run per charge (and
conversely, the longer it will take to recharge the pack). “Bigger number
= longer run time” is all you really need to know, but it’s helpful to understand what the mAh rating actually means. If your battery is rated at
5000mAh, that means it can hold a steady 5-amp load for a full hour. We
get “ 5” from “5000” because a milliamp is 1/1000 of an amp. Divide the
mAh rating by 1000, and you get amp-hours: 5000 ÷ 1000 = 5. If you have
a 6000mAh battery, it can hold a 6-amp load for an hour. Or, if the load is
3 amps, that 6000mAh will run for two hours. Greater capacity = longer
;e voltage of a battery pack is determined by how many cells it has. A
single NiMH cell delivers 1.2 volts, and NiMH batteries are most commonly
o;ered with six or seven cells. ;ese may be referred to as “6-cell” and
“7-cell” packs, or they may be referred to by their voltage: 7. 2 volts and
8. 4 volts (since 6 x 1.2 = 7. 2, and 7 x 1.2 = 8. 4). It’s di;erent with LiPos.
;e principle is the same, but since a single LiPo cell delivers 3. 7 volts,
LiPo packs have fewer cells for a given voltage. ;e most common
configurations are 2-cell, 7.4-volt packs ( 2 x 3. 7 = 7. 4) and 3-cell, 11.1V
packs. As with capacity, more volts is better—to a point. Your vehicle’s
power system is designed to handle a certain amount of voltage, and
exceeding that voltage will, at the very least, shut the system down if
it has “overvoltage protection” or, at worst, fry the electronics. Always
check your vehicle’s (or speed control’s) manual for the maximum
voltage specification before upgrading to a pack with more volts.
WHAT ABOUT “S”?
As we just discussed, NiMH and LiPo packs are often referred to by the number of
cells in the pack: for example, “2-cell” or “3-cell.” You may also see or read about LiPo
packs with a designation such as 2S, 3S, 4S, etc. In this case, the “S” refers to series,
and indicates that the cells within the pack are connected “positive to negative,” as in
the illustration at right. Some LiPo packs feature cells connected both in series and in
parallel, which is designated by a “P.” For example, a “2S2P” LiPo pack would have two
pairs of LiPo cells inside. Each pair would be wired in parallel (2P), and the two pairs would
be wired together in series (2S). Is your head hurting? Don’t worry about it. Nearly every
RC LiPo is wired in series and simply referred to as 2S, 3S, 4S, etc.
NIMH & LIPO
;ere are two essential types of batteries used to power electric RC cars
and trucks: nickel-metal hydride (NiMH) and lithium polymer (LiPo). ;e
chemistry-class names refer to the materials within the battery that
react to store and release energy as electricity, and each battery type
has its pros and cons.
If you purchased a ready-to-run (RTR) model with an included battery,
chances are it’s a NiMH. Nickel-metal packs are rugged, inexpensive,
and don’t require much in the way of special care. However, they’re
heavier than a LiPo battery of similar voltage and capacity (we’ll get to
those terms), and their voltage decreases more steadily as the pack is
discharged compared to a LiPo.
A LiPo battery is lighter than a NiMH of similar voltage and capacity,
which helps your model feel more powerful. Also contributing to that
“feeling of power” (often called “punch”) is the LiPo’s ability to maintain
higher voltage for a greater duration of its run time. ;e downsides are
cost (LiPos are more expensive than NiMH, but the gap is narrowing)
and durability (LiPos require a specific care regimen for longest life and
LiPo batteries are assembled with flat slab-like
cells, and a single LiPo cell is 3. 7 volts. ;is
pack has two cells, for a total of 7. 4 volts.
NiMH packs are constructed with cylindrical cells, just like what we
associate with the term “battery.” ;is pack is made up of six 1.2-volt
cells, for a total of 7. 2 volts.
;is Dynamite LiPo’s
capacity is 5000mAh,
;is illustration shows a 2S
pack: two 3.7-volt cells in series.
;e cells are connected by their
positive (+) and negative (-)
tabs to deliver 7. 4 volts at the