Cobra Libre (original, 2011) battery replacement

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asavage
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Cobra Libre (original, 2011) battery replacement

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Post by asavage »

I have an original series Cobra Libre, the one with the problematic touch controls. The later Cobra Libre II seems to have real buttons/switches, but the original has touch controls with no haptics. These are water-resistant or shower-friendly.

Original Cobra Libre (without buttons)
Original Cobra Libre (without buttons)
Cobra_Libre_Battery_Replacement_17b.jpg (73.3 KiB) Viewed 242 times

This thing was expensive back in the day, and I worried about battery replacement when I bought it. Fast forward to last month, it had been in the back of a drawer for years, and would not accept a charge. I could find almost no information about a replacement battery, nor how to disassemble it, except this YouTube vid, which ended up being very helpful, if out-of-focus :(

To replace the battery, you need to access the area under the silver end caps. The silver end caps incorporate o-rings for sealing, and lock into each other, not to the black housing. Here are the end caps removed, showing the dual-prong locking mechanism:

Cobra Libre: silver end caps, showing o-rings and dual-prong locking mechanism
Cobra Libre: silver end caps, showing o-rings and dual-prong locking mechanism
Cobra_Libre_Battery_Replacement_16b.jpg (799.44 KiB) Viewed 242 times


Here, you can see some of the damage I caused by prying first, before I twisted.

Cobra Libre: damage from trying to pry end cap off
Cobra Libre: damage from trying to pry end cap off
Cobra_Libre_Battery_Replacement_01b.jpg (2.4 MiB) Viewed 242 times


To unlock one cap from the other, I used slip-joint pliers ("ChannelLocks") and twisted (rotated) one cap about 5°, then pulled out. You can't pry or pull out directly, because the prongs are locked until you rotate one or the other cap. This is the damage caused by the slip-joint pliers to twist the cap:

Cobra Libre: damage from twisting end cap to disengage locking prongs, prior to pulling it off
Cobra Libre: damage from twisting end cap to disengage locking prongs, prior to pulling it off
Cobra_Libre_Battery_Replacement_14b.jpg (1.17 MiB) Viewed 242 times


In retrospect, I would have tried some smooth jaw curved pliers instead of the toothed jaw, but due to the beveled surface it's quite difficult to get a grip on the silver caps, so it may be that some plastic damage is inevitable. But only to one cap, and the sealing surface for the o-ring is not compromised by this method.

Once one end cap is removed, the other could be pushed out the other side. Neat.

Cobra Libre: end cap removed, showing packing
Cobra Libre: end cap removed, showing packing
Cobra_Libre_Battery_Replacement_03b.jpg (2.01 MiB) Viewed 242 times
Cobra Libre: first silver end cap removed
Cobra Libre: first silver end cap removed
Cobra_Libre_Battery_Replacement_02b.jpg (1.66 MiB) Viewed 242 times
Cobra Libre: end caps removed, battery slid out the bottom
Cobra Libre: end caps removed, battery slid out the bottom
Cobra_Libre_Battery_Replacement_15b.jpg (1.24 MiB) Viewed 242 times


A couple of square sponges fill the cavity and prevent rattling, followed by the prismatic battery, which has thin grey foam glued to it. Its connector can be removed from an interconnect PCB via needle-nose pliers. The empty fourth connector shown below, on the PCB, is where the battery connects. The battery & sponges pull right out. The blob on the right of this pic is the external magnetic-coupled charging connector:

Cobra Libre: showing battery connector on interconnect PCB
Cobra Libre: showing battery connector on interconnect PCB
Cobra_Libre_Battery_Replacement_05b.jpg (2.26 MiB) Viewed 242 times


The old battery showed physical damage.
Cobra Libre: original battery, showing damage
Cobra Libre: original battery, showing damage
Cobra_Libre_Battery_Replacement_06b.jpg (1.02 MiB) Viewed 242 times
Cobra Libre: original battery, showing damage
Cobra Libre: original battery, showing damage
Cobra_Libre_Battery_Replacement_07b.jpg (1.04 MiB) Viewed 242 times

Unfortunately, running the numbers on it through a search engine yields nothing. The charger is rated for 7.5v, so initially I thought I'd be looking for a 7.4v Li-ion battery, but nothing I could find at 7.4v looked to be the correct form factor.

What did look right was a 3.7v battery. I decided to roll the dice and get one. I bought this one via Amazon for $11:

EEMB 3.7V 1100mAh 603449 Lipo Battery Rechargeable Lithium Polymer ion Battery Pack with JST Connector

Remember: a Li-ion battery with onboard BMS is required, which rules out a lot of the RC batteries available.

Other than the connector, the EEMB battery was perfect. It has a JST-PH (2.00 mm pitch) connector, which is too large; I cut off the original battery's smaller connector and soldered it to the new battery.

Cobra Libre: old & new batteries compared
Cobra Libre: old & new batteries compared
Cobra_Libre_Battery_Replacement_18b.jpg (1.11 MiB) Viewed 230 times
Cobra Libre: battery connectors: JST 2mm on left, original on right
Cobra Libre: battery connectors: JST 2mm on left, original on right
Cobra_Libre_Battery_Replacement_08b.jpg (379.61 KiB) Viewed 242 times
Cobra Libre: cutting off connectors, solder original small connector to new battery
Cobra Libre: cutting off connectors, solder original small connector to new battery
Cobra_Libre_Battery_Replacement_09b.jpg (1.64 MiB) Viewed 242 times
Cobra Libre: connector swapped onto new battery
Cobra Libre: connector swapped onto new battery
Cobra_Libre_Battery_Replacement_10b.jpg (1.37 MiB) Viewed 242 times

Reassembly is just reconnecting the battery to the PCB, stuffing the battery and foam squares back in, and snapping the end caps together.
Cobra Libre: New battery connected and ready to insert
Cobra Libre: New battery connected and ready to insert
Cobra_Libre_Battery_Replacement_04b.jpg (3.52 MiB) Viewed 242 times
Cobra Libre: installing new battery
Cobra Libre: installing new battery
Cobra_Libre_Battery_Replacement_11b.jpg (2.48 MiB) Viewed 242 times
Cobra Libre: installing new battery
Cobra Libre: installing new battery
Cobra_Libre_Battery_Replacement_12b.jpg (2.91 MiB) Viewed 242 times
Cobra Libre: installing new battery
Cobra Libre: installing new battery
Cobra_Libre_Battery_Replacement_13b.jpg (2.19 MiB) Viewed 242 times


It seems to work and charge fine. I did not measure the smaller connector (I wish I had), but I hope this helps someone else resurrect an old Cobra Libre with a failed battery. These things are just too expensive to throw away.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
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