Battery Recharge

Our battery continues to have a much tighter difference between its max and min cell voltages than we did before we replaced supercell #10.

This is what a healthy battery looks like.

The Proof: We Actually Did Fix The Battery

It looks like despite the battery problems we had last week, our battery is healthy and doesn't have the one divergent supercell that we noticed during UNH testing.

You can also see the point at which we returned from dinner to find that the power supply had switched off.

Battery Scare in the 11th Hour!

While we were re-installing the battery into its glass sphere (after replacing the under-performing cell #10), there was a soft pop, a crackle, and then a hiss as clouds of tan smoke filling the air.

Some part of the battery had short circuited; something was seriously wrong!

We had to take the battery apart again to see what happened and to try and fix it. We are especially under the gun to fix this, because we are supposed to deploy on Monday to look for didemnum! Yikes!


The source of the crackle became apparent; it was the sound of a wire sparking and melting itself out of its jacket. You can see the bits of melted black jacket on the red wire.


There were some burn marks on the outside of the battery too.


But, the real damage was on the corner of the cell where the smoke forced its way out.

We count ourselves very lucky that only one supercell was damaged and that nothing caught on fire. In the end, we had to use the supercell that had been removed as the replacement for the one that was damaged (although we recharged it). A net gain in the end, but only a small gain.

REx II is Back in Cambridge

Today, we got the REx II vehicle back from Hawaii.

Due to restrictions on shipping, we didn't bother to send the lithium ion battery by mail. Instead, we just built a new one.


Unlike the battery for Odyssey IV, this battery is designed to fit into the bottom half of a pressure tube. The individual supercells are not wrapped in plastic, but instead squished together to form the full battery.


The electronics fit on top.

Installation of New Battery

The new battery has been constructed, and packed into its protective Nautilus sphere housing.

It appears to charge and discharge normally!

Battery Reconstruction Progress: 50%

12 of the replacement supercells (for our 24-supercell battery) have been completed. This time, we made better notes of the process.

Update: there is a new page on our wiki for the construction of a supercell.

Dead Battery

Our battery has failed.

After 3 years of faithful service, our battery was accidentally allowed drain far below the acceptable minimum voltage for Li-ion cells, effectively ruining its capacity. In fact, it would be unsafe to recharge this battery in its present under-voltage state.

We will have to build a new battery. This is unfortunate, but since these cells lose 20% of their capacity per year in perfect storage conditions, it was inevitable.

This will push our schedule back a bit...