To power my first e-bike, I bought a TLH 36V 15.6 Ah
Li-ion battery with charger. This came without
or instructions; but its operation seemed to be fairly
There is an LED status indicator that lights at the press of
button if the charger is plugged in and switched on, or if the battery
is switched on. A mounting plate and connector fits onto the
bike-frame down-tube, the
battery unit slides on to it and is locked into place using a
supplied key. An immediate issue I had with the Sterndale
frame however, is that there was only enough room for the battery on
the front down tube, and the battery-plate bolt holes were too high-up
to mate with the bottle holder attachment points. The work-around was
mount the battery upside-down. I also found that the heads of
M5 Allen screws that came with the bike were too proud to allow the
battery to slide onto the plate; and the solution was to
replace then with A4 stainless hex-head M5×12 screws
The mounting plate system allows the
battery to be
taken away for charging or
storage, but there is no obvious reason why it cannot also be charged
in situ. The battery charger gets quite warm
in use, so is best placed on a wire trivet, or a luggage
rack, or otherwise
suspended so that air can flow over it. Charging the battery
half to full takes about 3 hours; and the charger is small enough to
take with you if you are going somewhere with mains electricity. Once
charging is complete, the LED on the charger changes
red to green, and the charger cools down (indicating that the charging
current has been
My battery installation, unfortunately,
developed a major problem after a few days riding. This was
to do with the
electrical connection between the battery housing and the
mounting plate. Four flat pins on the plate mate with
the pack. I noticed during the installation that the four
were chromium plated. This is one of the worst conceivable
plating materials for a low voltage connector, because chromium has a
habit of forming a tough non-conducting oxide layer on exposure to
air. Still, the connectors were doubled-up, two for (+) and two
for (-), and so I put my initial doubts aside and presumed that the
arrangement must be OK in practice. Using the battery upside
however, it transpires that the connector is not quite as fully
inserted as it would be with the assistance of gravity. The
situation might also arise if the battery were to be mounted
horizontally. This no doubt contributed to the problem that
emerged, for which the symptoms were: random loss of power, and random
down of the system. It was
initially difficult to identify the cause, and the misbehaviour grew
and soon made the bike unusable. Eventually I worked-out what
happening by running the bike on a bike-stand and measuring the supply
voltage at the input to the motor unit. Random shut-down was
caused by large fluctuations in the on-load voltage, and the fault
reproduced by rattling the battery pack up and down on its mounting
plate. Careful inspection then showed that one of the
been getting hot and had started to melt the surrounding plastic. Also,
the connections are doubled-up, this indicates that its
partner was barely working at all.
Mounting plate and battery pack,
with signs of connector overheating.
I might at that point have decided to demand a
replacement battery, but that would not have solved the problem of
having to use it upside down. Also, I do not think that the
connector is fit for purpose, even if it is used the right way up.
I therefore decided to forfeit the warranty and solve the
by modifying the battery pack. I did that by installing a
female XT60 connector, which, as the name implies, is rated for 60
A. XT60s have gold-plated solid copper pins and receptacles
with a high contact area, and so have extremely low resistance.
Note that carrying out modifications to a vehicle battery
pack carries a risk of fire or explosion, and is therefore a job for a
competent electrical technician (please also see my Disclaimer
Battery pack with XT60
wired across the existing connector.
Note, on the enlarged image, that the legend (+) can be seen on
the plug adjacent to the red wire; i.e., the flat side of the
connnector denotes the positive terminal.
A small circuit board
can be purchased
for the XT60, enabling both the male or female types to be used as
bulkhead connectors. To prevent accidental short-circuits,
connectors on battery
packs must, of course, be female; so I fitted a board to a female
connector and mounted it on the battery case.
In doing that, I made a couple of pilot holes in the bottom
battery pack, and fashioned an XT60-shaped hole in the ABS using a
modeling knife and some small round and square rough-cut files.
When mounting the connector, I placed a couple of spacers on
the retaining screws, to minimise the protrusion, and sealed the
connector body into the hole I had made using architectural silicone.
I wired the XT60 directly across the existing connector,
thereby retaining the normal functionality (for what it's worth), and
also siliconed around the original connector to improve the
Finally, on reassembly, to minimise wateringress as far as
possible, I taped the join between the upper and lower parts of the ABS
housing. Note that it is possible to buy silicone rubber caps for female XT60
. These will exclude dirt and help to prevent
short-circuits in the event that the battery is stored or used on a
with the standard connector.
Having opened the battery pack, I had
an opportunity to make observations that would not otherwise have been
possible. I noticed that the On-Off switch is not capable of
handling the current required by the Bafang motor, and this function is
instead accomplished by using the switch to turn on a
transistor. Presumably, the cost of a small switch and a MOSFET is less
than that of a high-current switch. A somewhat worrying
feature however, is that plugging-in the charger also switches-on the
battery output,which is how the press-button battery-level indicator
comes to work either
when the battery is on, or
when the charger is in. This means that charging the battery while it
is installed on the bike has the effect of turning it on. The
bike, of course, does not wake-up unless the handlebar power button is
but it means that the the motor will not go to sleep straight away if
the charger is plugged-in before the battery is turned off.
Whether this is a serious issue is moot, but it is not ideal.
"Off" should mean "Off".
The appalling chromium connector
seriously coloured my initial impressions of riding the
bike. I came to the (very-pessimistic) conclusion that the
makes a rather feeble contribution to the rider's efforts, and while it
did (initially) enable me to get up the hill from Ottery without
stopping, I still had to do quite a lot of work. I also noted
that, while the twist throttle could start the bike from standstill on
level ground, it could not do so on a 5% gradient. The effect
of fitting the XT60 connector, and thereby discovering the actual
the motor, was consequently astonishing.
Although the following calculation
conjecture, we can easily get a rough idea of just how deleterious the
original connector was. If the Bafang BBS01 were to have a
peak power consumption of 250 W at 36 V, it would require a current
of 6.9 A. In reality however, if it is to deliver
W to the road, it needs a somewhat greater input than that,
probably approaching 300 W. This means that weshould expect
typical peak current of about 8.3 A, or say 8 A in round numbers.
Hence, in the state of maximum demand, the motor looks something like a
36/8 = 4.5 Ω resistance.
Now, if the connector were to have a
resistance in the region
of 1 - 2 Ω, then at times of peak power demand, it would be
expected to cause a voltage drop of between about 6.5 and 11 V.
Instead of a nominal 8×36 = 288 W input to the
motor, we would have
= 193 W and (36-11)2
= 139 W.
Approximately halving the motor power would indeed result in
performance, and the reduced voltage is likely to cause the controller
to assume the battery to be
dead and switch off.
When I built my second e-bike, I bought
model of battery again but fitted an XT60 connector immediately.
Links and additional info.
Li-ion battery packs.
Pedalease - TLH 36 V 15.6 Ah
: Where they came from and where
they're headed, by Anna Kučírková.
- Charging Lithium Ion batteries.
to e-bike battery connectors
- battery accessories, connectors, caps,
Building an e-bike battery from 18650 cells.
the purpose of making comparisons between the various battery
options, that some e-bike and battery manufacturers give the capacity
in Watt hours (Wh). Since power is given by voltage ×
simply multiply the capacity in Ah by the nominal voltage to get the
figure in Wh. Thus a 15.6 Ah, 36 V battery (used with the Bafang BBS01)
is a 562 Wh unit
(rounded to the nearest whole number because the voltage is nominal and
varies throughout the discharge cycle). This is a lot bigger than the
batteries fitted to some commercial e-bikes, and there is now (≥
Oct 2019) a 20.4 Ah (734 Wh) version available.