Don’t charge it up all the way(?); wattage and 80/20 advice.

So I have some experience charging lithium ion batteries with work I have done on remote cameras. The “common knowledge” regarding these batteries is that if you want to get the most life out of the batteries, only charge them up to 80% of  their capacity and don’t drain the past 20%. This is common to Tesla owners as these are the same size batteries (Panasonic 18650)  that can be found in some models. The Tesla interface encourages you to stick to the 80/20 rule to prolong battery life. I have not heard or read anywhere that Specialized has recommended this rule to their users of the Levos. Perhaps the message would be too confusing for this emerging product.

To try to find out a bit about this I set up an experiment to monitor the consumption of power that the Levo charger was pulling during charging. First, I rode my Levo until it had 1 red bar showing. I then waited a few hours and hooked up a watt meter and a temperature gauge to the charger and started my experiment.

excel

The results show a steep drop off in wattage at about 120 mins into the charging cycle. This roughly coincided with the 8th green LED staying lit and the 9th starting to blink. You can deduce from this that you get about 80% of your charge in the first 66% of the charge time, the last 1/3 of the time you are only putting in 20% of the total charge.

The temperature of the battery did not change while charging, and if you have this happen it’s certainly a reasonable concern – but the charger itself was a different story. It started at room temperature and then rose to toasty 136 °F (58C°). I have felt this before – but it’s good to quantify it.

Another reason for this experiment came from an experience that I had last weekend where we were “off the grid” and wanted to charge our Levos. We did not know how many watts the battery/charger would draw. The battery itself says that max output is  168 watts (amps x volts = watts), with a peak draw of 190 watts observed from the experiment, the charger is about 88% efficient.

Another interesting tidbit that I gathered from the experiment was the cost of charging the battery – in California electricity is a bit expensive, the average residential electricity rate of 15.34¢/kWh in CA is 29.12% greater than the national. Still even at this rate the largest battery that Specialized makes, 691 WH, would cost you about 11 cents to charge. Viva la Levo !

It’s been noted that this charging scheme is not too realistic for many users – just plug it in and ride, but keep these tips in mind:

  1. Don’t leave your Levo fully charged when in storage – 80% is good – this is how Specialized delivered my Levo.
  2. Charge your battery every three months as it can cause damage to the battery – this is the manual.
  3. My bike shop told me to once a month leave the bike plugged in overnight – this may be for balancing the cells – not sure. The manual says not to leave the charger connected “for extended periods” after the battery has been charged. Hmmm…

Viva la Levo !

 

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