此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采取“小心駛得萬年船”的策(ce)略(lve)，用(yong)(yong)小電(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)，一般不超過100mA ，這樣電(dian)(dian)(dian)(dian)池充(chong)(chong)到最后，發熱不至于太大(da)(da)，從而延長電(dian)(dian)(dian)(dian)池壽(shou)命(ming)。缺點是充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間(jian)長。現在生產(chan)這類的廠家(jia)，采用(yong)(yong)中電(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)，100～200mA 充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間(jian)大(da)(da)大(da)(da)縮(suo)短，但是以犧牲電(dian)(dian)(dian)(dian)池壽(shou)命(ming)為代價。傻(sha)瓜型充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)只能用(yong)(yong)時(shi)間(jian)來控(kong)制充(chong)(chong)電(dian)(dian)(dian)(dian)，它只適合(he)于深(shen)充(chong)(chong)深(shen)放的五(wu)號(hao)(hao)、七號(hao)(hao)鎳(nie)(nie)鎘、鎳(nie)(nie)氫(qing)電(dian)(dian)(dian)(dian)池。

    充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時間：T = 1.5C/I（ C是(shi)電(dian)(dian)(dian)(dian)(dian)池容量，I是(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流）例：如果有(you)個1000mAh 的電(dian)(dian)(dian)(dian)(dian)池放(fang)在充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流是(shi)50mA的充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器上充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時間就是(shi)30小時。辨認這類充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器的方法：當插上電(dian)(dian)(dian)(dian)(dian)源插頭后，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)指示(shi)燈一直亮著。街上賣的10～40元以內的均是(shi)這種充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器。