The four AA size Nickel Metal Hydride (NiMh) batteries in the AquaCalc Pro Plus (APP) are sized so that you can get more than one full day of work out of the unit . Battery life on the AquaCalc Pro Plus is about 10 hours under normal conditions using the supplied 1900 milliAmp-hour (mAh) Nickel Metal Hydride (NiMh) rechargeable batteries. Using the USB connection to charge these batteries in the AquaCalc takes about ten hours. We recommend that you carry spare batteries into the field.
There is a sticker in the battery compartment of the AquaCalc Pro Plus (APP) that says something like “NiMh Batteries Only”. We were a little too aggressive with the warning about using alkaline batteries. The AquaCalc Pro Plus can take over -the-counter alkaline batteries, just like the old AquaCalc Pro. But, alkaline batteries should not be charged. If you leave them in accidentally, and plug the unit in to download, they will eventually grow hot and leak, damaging the APP.
If you no longer wish to charge the NiMh batteries in the APP to avoid the possibility of damaging the APP with leaky alkaline batteries, you can disable the charging circuit in the APP:
The batteries shipped with the AquaCalc Pro Plus are Nickel Metal Hydride rechargeable batteries with 1900 mAh capacity. You can purchase NiMh batteries with greater capacity than those we provided. Sanyo makes a “Enerloop XX” NiMh AA battery that has a capacity of 2500 mAh versus the 1900 mAh that we ship as standard. The existing batteries take about ten hours to fully charge in the APP, these larger ones will take longer. You can purchase these batteries from JBS Instruments, or Amazon:
We also recommend that you replace your batteries annually. With repeated charge and discharge cycles, NiMh batteries can degrade and the operating voltage decrease. Over time this will result in shorter battery life and the time needed between charging.
As you know, cold changes everything when it comes to equipment, especially batteries. While the APP hardware is designed to work down to about five degrees F, the batteries don’t.
The biggest problem with batteries in the cold is that the chemical processes in the batteries stop when they get cold enough. Carrying warm spares in your pocket can help when the batteries in the APP get too cold to work. The APP uses standard rechargeable NiMh AA batteries, any brand should work. We like the Sanyo Enerloop brand because they have a lower “self-discharge” rate, meaning that they won’t lose as much capacity when they just sit around. Some cheaper brands lose capacity as they sit. Keep spares warm.
One of the advantages of the AquaCalc Pro Plus’s USB port, is that it can be powered through this port. This means that you can add an external battery pack to the APP, and keep the battery pack in your pocket, connected to the APP via a USB cable. The batteries stay warm.
One of our customers near Mt- Shasta has been testing this for us and is pleased with the result, he reports that it is best if you remove the batteries from the APP, so that when they get cold they don't drag down the warm batteries in your pocket. So far we have tested two types, both work. One uses your spare AA NiMh batteries and can charge them, the other uses a built-in Lithium Ion battery and has more capacity. These can be purchased from JBS Instruments, or Amazon:
We would be interested in you results when testing these.
We recommend that you replace batteries every year. Old rechargeable batteries can perform poorly. We tested a used AquaCalc Pro Plus 14050264 with new 1900 mAh batteries (which ran for 11.5 hours), and older used customer batteries (which ran for 7.25 hours). The normal power draw for an AquaCalc Pro Plus is between 0.13 and 0.17 Amps.
Note the initial drop off in voltage slows at about 5.1 volts and then “plateaus” and slowly falls to 4.85 before picking up pace and exhibiting the standard S curve. After the AquaCalc shuts off, the battery voltage rises slightly as the batteries recover.
Methodology: After charging the batteries to full (which takes about 14 hours), the AquaCalc was set to Auto-Pwr Off” to “Never” power off, placed in the Measure screen with meter beeps turned on, connected to a rotating pygmy current with a AquaCalc Digital Pygmy Magnetic Head, and run continuously until it shut itself off. In the 14050264 1900 mAh battery unit brand new fully charged batteries were used. The test was run at a room temperature of about 78 degrees.
Note that in older batteries, the initial voltage will fall much lower, and the entire plateau will shift lower, below 4.7 volts, causing the the AquaCalc to shut off sooner before it reaches the voltage “tail”.