Using a Lithium Ion Battery to replace NiMH For Welch Allyn Otoscope/Opthalmascope

BATTERY Welch Allyn
COST $60 CDN $15 CDN
WARRANTY 2 Years 1 Year
HOURS OF USE 1 unit 5 unit
CHARGE TIME 16 hrs 4 hrs
CHEMISTRY Nickel Cadmium Lithium Ion
VOLTAGE 3.5 V 3.6 V
mAh 620 mAh 3400 mAh
LIFE SPAN 2 yrs 10+ yrs
WIDTH x HEIGHT 1″ x 2.9″ 0.73″ x 2.57″ (18.90mm x 69.41mm)

Over the years our Simulation Centre had quite the challenge of ensuring that our otscope/opthalmascope handles had enough power to endure a busy week of ear/eye skills lab. Often times batteries would fail to endure a 3 hour skills session. This would draw the ire of faculty and students alike. We could have chosen to purchase more batteries or handles but we felt that having users switch battery or handle partway through their lab would be a bit of a hassle. So in the summer of 2017 I went on a quest to look for a solution. How difficult could it be!

The current battery technology used by Welch Allyn for their handles is of bygone years. Nickel Cadmium batteries haven’t been used widely in portable electronics for a couple of decades. Lithium Ion batteries are now King. The wide use of Li-Ion over the years has seen the price come down considerably. Li-Ion batteries can be found in the Tesla, portable computers and many cordless power tools. Li-Ion batteries are cheaper, have a greater energy capacity and it has up to 5 times the lifespan of NiCd. Surely there must be a Li-Ion replacement for the 72300.

Replacing the 72300 is not that easy. Substituting one battery technology for another is not as simple as finding an equivalent battery size and plugging it in. For one, NiCd batteries have a nominal rating of 1.2 volts per cell where as Li-Ion have a nominal voltage of 3.6 volts per cell and typically max out at 4.2 volts, which is well over three times the voltage of the NiCd cell. Considering the 72300 has a voltage rating of 3.5 volts, which is almost 3x that of a NiCd cell, it would appear that the 72300 is a custom cell created by Welch Allyn, composed of three cells stacked one on top of the other in series and packaged in a cylinder resembling a elongated d-cell. With only a 0.1 volt difference between the 3.6 v, single cell Li-Ion battery and the 72300 NiCd, finding a replacement was made a little easier. More than likely the format of the 72300 is not used by other manufacturers of medical assessment handles. The 72300 is a non-standard format, it was not found in the International Electrotechnical Commission (IEC) or the American National Standards Institute (ANSI) specifications.

I scoured the internet for a replacement Li-Ion battery close in size but not bigger, since it has to fit into the handle. Many of the cylindrical Li-Ion batteries came close in length but not in width. Not only was I looking for the greatest capacity for a chosen size but one that wouldn’t produce 25 Amps if a short was accidentally made during handling. Here comes protected cells to the rescue. Protected cells are Li-Ion cells that have a control circuit attached to the end of the cell. The purpose of the circuit is to protect the cell against short circuits, over charging and over discharging.

The Panasonic NCR 18650B Lithium Ion battery was chosen for the most crucial component – the protection circuity (don’t want batteries catching fire or exploding in students or professor’s faces). The circuit limits the current to 4.875 Amps which is still a bit much for my liking but compared to the alternative there is no other option. The NCR18650 is rated at 3400 mAh, which is quite impressive for it’s size. The numerals in the part number 18650, refer to the width of 18mm and length 65.0mm. There is quite a difference in the size of the 72300 and the 18650. The 18650 is smaller by 4.3mm width-wise and 6.5mm length-wise. The most concerning of the 2 numbers being the width. The last thing I want is for the battery to be moving about inside the metal handle with the potential for a short to occur.

Panasonic Li-Ion Battery NCR 18650B Datasheet

The spring inside the cap of the handle made it easy to overcome the difference in length and secure electrical contact. However, to keep the battery from moving side to side I purchase a 1″ x 2″ PVC Riser from Home Depot. The inside diameter matched the Panasonic NCR18650 perfectly. However with most mass produced products, outside of precision components, the outside diameter varied from perfect fit to snug to completely impossible. I needed a total 16 spacers, however half of them were slightly thicker than 1″, so I sanded them down with #80 grit sand paper. Each took about a half hour of hand sanding.

Battery Assembly

Battery inside PVC Riser inside handle

One thought on “Using a Lithium Ion Battery to replace NiMH For Welch Allyn Otoscope/Opthalmascope”

  1. What’s up?

    I found this article very interesting…please read!

    Do you remember the blockbuster hit film The Matrix that was released in 1999? You may not know this, but it has deep spiritual implications concerning the times we are living in and Bible prophecy.

    It tells a story of how these “agents” are trying to turn us into machines. We are closer then ever before for this to become a reality when they cause us to receive an implantable microchip in our body during a time when physical money will be no more.

    You may have seen on NBC news concerning the implantable RFID microchip that some people are getting put in their hand to make purchases, but did you know this microchip matches perfectly with prophecy in the Bible?

    “He (the false prophet who deceives many by his miracles) causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads, and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name…

    You also may have heard of the legendary number “666” that people have been speculating for possibly thousands of years on what it actually means. This article shares something I haven’t seen before, and I don’t think there could be any better explanation for what it means to calculate 666. This is no hoax. Very fascinating stuff!

    …Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666″ (Revelation 13:16-18 NKJV).

    To see all the details showing why the Bible foretold of all these things, check out this article!


    GOD is sending out His end time warning:

    “Then a third angel followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives his mark on his forehead or on his hand, he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb. And the smoke of their torment ascends forever and ever; and they have no rest day or night, who worship the beast and his image, and whoever receives the mark of his name” (Revelation 14:9-11).

    In the Islamic religion they have man called the Mahdi who is known as their messiah of whom they are waiting to take the stage. There are many testimonies from people online who believe this man will be Barack Obama who is to be the biblical Antichrist based off dreams they have received. I myself have had strange dreams about him like no other person. So much so that I decided to share this information.

    He came on stage claiming to be a Christian with no affiliation to the Muslim faith…

    “In our lives, Michelle and I have been strengthened by our Christian faith. But there have been times where my faith has been questioned — by people who don’t know me — or they’ve said that I adhere to a different religion, as if that were somehow a bad thing,” – Barack Obama

    …but was later revealed by his own family members that he indeed is a devout Muslim.

    So what’s in the name? The meaning of someones name can say a lot about a person. God throughout history has given names to people that have a specific meaning tied to their lives. How about the name Barack Obama? Let us take a look at what may be hiding beneath the surface…

    “And He (Jesus) said to them (His disciples), ‘I saw Satan fall like lightning from heaven'” (Luke 10:18).

    In the Hebrew language we can uncover the meaning behind the name Barack Obama.

    Barack, also transliterated as Baraq, in Hebrew is: lightning

    baraq – Biblical definition:

    From Strongs H1299; lightning; by analogy a gleam; concretely a flashing sword: – bright, glitter (-ing, sword), lightning. (Strongs Hebrew word H1300 baraq baw-rawk’)

    Barak ‘O’bamah, The use of bamah is used to refer to the “heights” of Heaven.

    bamah – Biblical definition:

    From an unused root (meaning to be high); an elevation: – height, high place, wave. (Strongs Hebrew word H1116 bamah baw-maw’)

    The day following the election of Barack Obama (11/04/08), the winning pick 3 lotto numbers in Illinois (Obama’s home state) for 11/5/08 were 666.

    Obama was a U.S. senator for Illinois, and his zip code was 60606.

    Seek Jesus while He may be found…repent, confess and forsake your sins and trust in the savior! Jesus says we must be born again by His Holy Spirit to enter the kingdom of God…God bless!

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